Food contaminants and gastrointestinal or liver neoplasia

Food

Contaminants

and

Survey

Gastrointestinal

of Experimental

or Liver

Neoplasia

Observations

ff. F. lG3.4~~11,~

Frequent reference has been made to the role of nutrition and dietary factors in carcinoqenesis ( 1, 2 ). Recently, much attention has been focused on investigac tions dealing with the increasing number of chemicals and the hazards to man of these chemicals in his modern environment. These studies have elicited a bodi of knowledge and data on chemicals detected as toxic components in certain human foods, medicines, and animal feeds, which have exhibited carcinogenic an d mutagenic responses in various test systems. Many of these naturally occurring compounds and those produced in food processing or as additives are hepatocarcinogenic in rodents and other test species (3-5). Elucidation of the mechanism of action of these tumorigenic and carcinogenic food contaminants in natural products has stimulated extensive toxicological research and provided suggestive evidence for extension of epidemiological studies, particularly as it relates to gastrointestinal carcinoma in man. In the following discussion, consideration will be given to delineating the experimental evidence available on these various food contaminants and additives and the implications to human carcinogenesis. CAHCINOGENS

ASSOCIATED

WITH FOOD ADDITIVES DEGRADATION PRODUCTS

A. POL~CXCLIC

AND FOOD

PROCESSING

HYDROCARBOXS

It has previously been indicated that high temperature pyrolysis of foods ma? give rise to carcinogenic polynuclear aromatic hydrocarbons (6, 7). These polynuclear hydrocarbons have been identified in charcoal-broiled meat, smoked foods, and in “coffee soots”, a by-product produced in commercial roasting of coffep beans ( 8). The latter finding has suggested that these hydrocarbons might also be found in commercial roasted coffee and indeed such has been demonstrated to be the case (9 ) . Hueper and Payne (8) have reported that precancerous lesions and benign and malignant neoplasms of the skin. connective tissue. stomach, and bladder developed in mice, rats, and guinea pigs respectively. after their exposure to soot from coffee-roasting plants. From their critical analysis of experimental and epidemiologicnl data they did not attribute these affluents from coffee-roasting plants in New Orleans as a major factor in cancer induction among the resident popu231 @ l!K!l t)y ;\cndrmic Prrss, Inc..

232

H.

F. KEUYBILL

lation of that city. As an air pollutant, however, they did not dismiss these compounds as potentiating agents. Dichloromethane and hot water extracts of various brands of roasted coffee were analyzed by Kuratsune and Hueper (9) and revealed predominantly the presence of pyrene and fluoranthene, but some benzo[a]pyrene was recovered from a particular brand of an extremely dark roasted coffee. The approximate concentrations of some of these hydrocarbon fractions are shown in Table I. TABLE POLYCYCLIC WITH

Brand Compound

I*

AROMATIC HYDROIXRBONS IN DICHLOROMETHANE AND WATER

DCMX’

(pg/kg

EXTRACTED

of coffee)

A HzOX2

Pyrene Fluoranthene Benz[a]anthracene Chrysene Perylene Benzo[e]pyrene Benzo[u]pyrene Benzo[k]fluoranthene Benzo[yhi]perylene * Adapted from Kuratsune and Hueper (9), 1 DCMX-dichloromethane extract. 2 H,OX extract,. 3 DCM extract of instant coffee. 4 Brand D-extremely dark-roasted coffee.

COFFEE

Brand B DCMX3

Brand D4 DCMX 17 15 0.5 2.0 0.8 3.0 4.0 0.8 4.0

(1960).

Hence, brewed coffee could be one of many various sources from which polycyclic aromatic hydrocarbons reach the gastrointestinal tract. A person drinking five cups of coffee daily, according to Kuratsune and Hueper (9)) could ingest about 0.4 pg of pyrene and 0.1 pg of benzo[a]pyrene. If other brands of coffee are used the intake will be considerably less or absent. However, other foods, such as smoked foods, contain these hydrocarbons, as is the case with charred dough from excessive baking or toasting, tobacco tar, paiaffin oil used medicinally, and paraffin wax used on food containers (9). In the preservation of foods, smoking procedures have had a long history of use. Smoked foods have been shown to contain a wide spectrum of polycyclic hydrocarbons, including a major carcinogen such as benzo[a]pyrene. In Tables II and III the concentrations of these polynuclear hydrocarbons are shown in charcoalbroiled steaks and in smoked mutton and fish. In Table II, the total level of hydrocarbons is presented for fifteen steaks. Dungal (10) indicated that the level of benzpyrenes in 1 kg of smoked mutton corresponds to the quantity contained in the smoke condensate of 250 cigarettes and Lijinsky and Shubik (7) state that benzo[a]pyrene to the extent of 9 pg per steak (Table II) is equivalent to that level of benzo[a]pyrene in the smoke of approximately 600 cigarettes ( 11). No nitrogen heterocyclic compounds weie detected in the charcoal-broiled meats,

FOOD

CONTAMINANTS

AND

LIVER

TABLE II* HYDROCARBONS IS CHARCOAL

POLYNUCLEAR

233

NEOPLASW

BRoIT,Er)

*r~ax5

Concent,ration Total h’

Per steak

Per kilogram

IBenzo(a]pyrene

133.0

9.0

s.0

Benzo[e]pyrene Chrysene Coronene D’l i )ellz[ah]anthr:lcell~ Fluoranthene Phennnthrenr Pyrene Perylene

97.0 21.0 37.0 3 .i 3’1 .o 180.0 286.0 34 0

6 .i 1.5 2.5 0.2 21.0 12 0 190 2.0

60 1.l ‘2 :: 0 2 20 0 11.6 1x.0 2.0

Compound

* From

TJijin~ky

and Shuhik

in pg Per 100 cm!

(7 I, (1964’1.

indicating that perhaps the meat protein is apparently not pyrolyzed but that the most likely source of the hydrocarbons is the melted fat which drips on the hot coals and thence undergoes pyrolysis at the high temperature. These hydrocarbons arc deposited on the meat as the smoke rises. It is assumed that oven broiling or roasting of meats would be less likely to produce the carcinogenic b!-drocarbons. None of these investigators make any broad speculation as to the epidemiological significance of these food contaminants through processing or heating, although the conclusions reached by Dungal (lo), and Kuratsune and Hueper (9) point clearly in this direction. The incidence of neoplasms, particularly gastrointestinal

POLYCYCLIC

AROMATIC

Concentration Hydrocarbon

in micrograms

Mutton

Acenaphthylene Fluorene Phenanthrene Anthracene Pyrene Fluoranthene 1,2-Benzpyrene 3,4-Benzpyrene * From

TABLE III* HYDROCARBONS IN VARIOUS

Bailey

187.7 20.6 86.5 19.8 5.9 4.6 0 1.3 and Dungal

(6),

(1958).

per kilogram

SNOKED

of wet

tissue

FOODS of various

foods

Trout

Redfish

Cod

83.0 31.1 41.8 13.1 4.9 0 0 2.1

4.3 0 5.0 1.5 3.0 4.0 0.3 0.8

0 0 0 1.8 0.7 0.5 1.9 0.5

234

H.

F.

RRAYBILL

cancer for Baltic or Icelandic fishermen eating smoked fish, is three times that for inland populations or for populations such as those of individuals of Scandinavian extraction in LISA on a nonsmoked fish diet. Stomach cancer incidence in Iceland represents about 35-45% of all malignant tumors. Dungal’s conclusions have been considered by other investigators (9) and it has been pointed out that there ;Ir(’ no complete data on magnitude of intake of the carcinogenic aromatic hydrocarbons by all comparative groups for study, a1ld that it is not known what the threshold level for man is in terms of daily or lifetime exposure or ingestion requisite in producing r gastrointestinal carcinoma; nor is it known what physiologic action the digestive tract would have on these compounds or what other factors may directly or indirectly influence the induction of cancer in the alimentary tract. Voitelovich et al. (12) reported data which tended to show a statistical relationship between high incidence of gastrointestinal cancer and frequent consumption of smoked fish. B. FOOD ADDITIVES

(Colorants,

Flavoring

Materials

and Pesticides)

Certain dyes used to enhance the color of foods have been proven toxic and in some instances, carcinogenic, in feeding experiments with rodents, and accordingly these materials have been banned for further use. Some sweetening agents such as Dulcin or I)-phenetylurea have been shown to be toxic and capable of producing liver cancer in experimental animals ( 13, 14 ) . Most flavoring agents are not carcinogenic. However, a plant material such as oil of sassafras or safrole (p-ally1 methylenedioxybenzene) has been shown to he hepatocarcinogenic when fed to rats in a diet for 67 weeks at a level of 0.5% (15). Safrole was used mltil recently as a flavoring agent in soft drinks such as root beer and sarsaparilla. Diets containing similar amounts of dihydrosafrole in which the ally1 group is saturated were foulid to produce esophageal cancers in the rat but not cancers of the liver. Safrole occurs as a constituent of essential oils of cinnamon, nutmeg, and mace, and has been made synthetically. Safrolc use has hecn discontinued as a flavoring agent in soft drinks. No action has been taken rclativc to use of cinnamon or mltmeg or other natural products containing ion- lcvcls of safrole. Dietary factors ma!- enhance or protect a,qainst carcinogenic or toxic cffects of safrole ( 16). Some pesticides which could appear as contaminants in food as residues ha\-cl lx:n denied clcarancc for use because of their carcinogenic properties. Aramite usc,d for control of mites in certain fruit crops has been applied in this country at a level of 1 ppm. This chemical ( 2- [p-tert-butylphenosyl] isopropyl-2-chloroethysulfite) contains a small amount of 2- ( p-terf-l~utylphenosy ) isopropyl sulfite. In feeding experiments with rats, dogs. and mice, this compound was found to be hepatomatous ( 17, 18 ). A zero tolerance has therefore been set for food crops. It is currently used on nonfood crops. The use of the fungicide thiourea and thioacetamide on citrus fruits has been discontinued since they were found to produce liver cancer in rats ( 19). Some pesticides, especially the persistent organoohlorine insecticides, are only slowly metabolized or mobilized from the adipose tissue and accordingly have a long residence time in human tissue. Dieldrin, an eporide, has been demonstrated to be a tumorigen in experimental

FOOD

COiYTAhIINAA'TS

AND

LIVER

SEOPLASIA

235

animals (20) but thus far neither DDT nor any of the other organochlorine type compounds have been established as carcinogens in animals or man. Further, long-term studies in animals and epidemiological surveillance in man will bc necessary to delineate whether this constant challenge at the cellular level has adverse effects. XATURALL‘I-

A.

OCCURRING PLAXT

AND

SEED

CARCINOGENS TOXICANTS

1. CycarIs and Cycasin In tropical and subtropical regions, natives have utilized cycad nuts as emergency and staple foods as well as a medicine but they have long been recognized to contain components toxic to livestock and man. These toxins can be extracted with water in the preparation of an edibIe starch. Japanese al)d AustraIian investigators have isolated and characterized the toxic components in cycad nuts which are a series of glycosides, the most common of which is cycasin. A common aglycone of the glycosides is methylazoxymethanol, which has been isolated and synthesized (21, 22). Severe liver damage may result from ingestion of either the toxic cycad nuts, cycasin, or methylazoxymethanol. Because of the high toxicity and high incidence of certain neurological diseases in arcas where natives ingested these materials as sources of foods and medicines, extensive studies were initiated in experimental animals. When toxic cycad nut meal was fed to rats for several months at a few percent in the diet, a high frequency of primary tumors in the kidney and liver developed (23) even after the animals were returned to a control diet (a). Variations in the deglucosylating activity of various intestinal bacteria may account for the differences in toxicity of ingested cycasin ( 25). In rats the pyrrolizidine alkaloids, cycasin and aflatoxin, all produce irreversible liver effects after only a short time exposure early in the life cycle. It may be, therefore, that these products are relevant to gastrointestinal oncogenesis in humans. 2. Pyrroliziclinc

Alkaloids

LInti aflatoxin had been delineated as the etiologic agent in lethality of turkey poults in England, the pathogenesis of this turkey S disease was such that the tosic source was ascribed to Senecio alkaloids. In fact, the pathological aberrations caused by aflatoxin, the fungal metabolite of A. J%IWS, may be indistinguishable from sencciosis. Schoental (26) has demonstrated the carcinogenic action of the pyrrolizidine alkaloids derived from Crotolnriu, which have a Lvide distribution. Because of the high hepatotosicitv and hepatocarcinogenicity of the pyrrolizidine alkaloids, this has given rise to the suspicion that natives drinking “bllsh teas” in certain areas of Africa south of the Sahara may present a high incidence of liver disease and hepatocellular tumors because of these carcinogenic agents. As will be discussed later, aflatoxicoses and other factors may be involved, so it is difficult at this point to ascribe a definite etiolopic agent such as the &n&o alkaloids in these liver diseases in man.

236

H.

F. KRAYBILL

3. Other Seed Products Certain plants in the genus Laburnum have been found to contain thiourea in the seeds. Thiourea, an antithyroid compound, was found to produce thyroid adenomas and carcinomas, and benign liver tumors, when this compound was administered to the rat ( 19). 4. Fern Species-Bracken In Japan a plant, zen mai (Osmunda japonica), is used as a vegetable and for seasoning purposes. It so happens that this plant is similar to the bracken fern and because of this it has been suggested that the high incidence of gastric carcinoma among the Japanese could be attributed to this toxic bracken fern material. This supposition is based on the fact that a diet containing 34% of dried bracken fern, when fed to rats, produced multiple adenocarcinomas of the small intestine (27). 5. Selenium Compounds It has long been recognized that selenium is an essential nutrient for certain mammals and avian species. On the other hand, compounds of selenium can be either hepatotoxic or hepatocarcinogenic. Selenium in the soil incorporates into plant material partly as selenomethionine or selenocystine. Livestock consuming high levels of forages with these seleniferous derivatives experience toxic symptoms but at low levels or deficiencies in the soil the reverse is true in that deficiency diseases result. When rats were fed selenium in the form of selenate, or selenide, or seleniferous corn or wheat in the diet at a level of 5-10 ppm for many months, hepatomas were induced (28). Miller (5) has indicated that abnormal selenoproteins might play an important role in the neoplastic process and in view of our current knowledge on alkylation of nucleic acids one might consider the possibility of abnormal methylation of cellular constituents by a compound such as selenium adenosylselenomethionine. 6. Bacterial

Metabolites

Another interesting fact has been uncovered in bacterial metabolism with the discovery that ethionine, the S-ethyl analog of methioninr, could be produced as a metabolite of E. co7i in a salt glucose medium containing sulfate ion or methionine ( 29). This synthetic carcinogen was discovered through tracer studies (30). This carcinogen would be expected to produce hepatomas through action at liver sites on nucleic acids. It is not known to what extent mammals or man are exposed to this bacterially synthesized carcinogen, which could occur in the caecum or the large intestine. This suggests an interesting study to search for the presence of this compound and a first approach might be through examination of rumen contents or milk of ruminants as recommended by Miller (5). 7. Mycotoxins-Fungal

and Mold Metabolites

One of the most interesting episodes in the field of mammalian and avian toxicity and oncology has transpired in the last 5 years with the development of

FOOD

CONTAMIXAXTS

ASD

LIVER

SEOPL4SIA

237

knowledge concerning some steps in the pathogenetic actions of ~1. flavus toxin, or later called by the British aflatoxin, which has far reaching implications in terms of the etiological relationship to man, The stimulus for this interest wu the occurrence of turkey X disease in the south and east of England where 100,000 turkey poults have died from what was later found to be the result of ingesting A. flnvus-contaminated Brazilian peanut meal. Subsequent studies in rats, where toxic peanut meal was fed at 20% levels in the diet or at a concentration of 6 ,cg daily of aflatoxin, revealed that this compomld was capable of inducing hepatomas in 30 weeks (4, 31, 32). The significant problem, perhaps of greater relevance to man, is the indirect invasion of an organism \vhich results from fungal growth taking place externally and its subsequent ingestion via animal or humall foods as the hepatotoxic and hepntocarcinogenic mycotosin. By direct exposure. for example, in 26 cases of secondary aspergillosis found at autopsy, in 7 of which the fungal infection was a contributing factor to death, there was no evidence in any of the 26 cases of liver lesions or hcpatomas even though it is known that A. flues can produce the hepatotosin under appropriate conditions (33). For man!; years, molds have been known to produce mctabolites but the pathogenetic potential of these mold metabolites in animals and human diseases has been obscure or overlooked. In general, the possibility that mycotosin contamination of food is endangering the health of human beings is of great concern in the Far East and -4frica. Slycotoxins from Penicillium islantlictm inhibit growth of Chang’s livcbr and HeLn cells and at high enough concentrations lead to morphological chan%esand dcnth (34). Also, the endotoxin extracted from the m),celia of A. frr~igat~v affected the respiration and produced morphological changes in kidney tissue ( 35). As to mechanism of action, the aflatoxin in tissue culture suppressesmitosis and inhibits DNA synthesis, which results in giant cell formation somewhat like the action of alkylating agents (36, 37) and chromosomal effects have been reported by action of a&toxin on human embryo cells (38) and blood cells (39). :1nother antibiotic, citrinin, produced by P. idantlic~rnl on feeds or ycllo~~l rice imported from Japan, could produce renal and hepatic toxicity and hence this compom’cl is not used therapeutically. Primary hepatoma may be prodllccd b!- this compound in roclcnts (40). It is quite significant that the general relationship between mold contamination of foods and feeds and disease syndromes in animals especially, and man as well, has been stressed in reports since the b~kginning of the nineteenth century but clinically they were largely ignored (41). Four biologically active compounds of aflatoxin arc produced by A. flul;z~s and identified as B,, G,, Bz, and G,, with their acute toxicity being in that descendill? order. Many biological systems have been used to demonstrate the high degree of toxicity of the aflatosins, including nonhuman primates, to demonstrate their potential hazard to man. The acute toxicity data given on aflatosin for the spectrum of species tested should serve as a guideline for potential hazard of a continuous chronic or subchronic ingestion of this factor in the human diet. .$ comparison of the relative toxicities of some well known hepatocarcinogens is given in Table IV. Another point that must be kept in mind is the extreme susceptibility of' the young. and the effect of aflatoxin on the pregnant mammal, This becomes

238

H. F. KRAYBILL TABLE COMr.4RIsON WITH

OF C'ARUS~OENIC

!LFLATOXIN

I
IT’

DOSE FOR

IL~TES HEI'BTOMA

OF VARIOUS

Co~~or-s~~s

PROTXYTIOX

IN

Tumor

K.4~8

d:ttn -.

Approximate Induction period ida,ysJ

Frequency (%I

IO,? “lx

JO0 64

1'20

120

100

1x0

1x0

dOX

Compound p-tliInethylamilloazol,el~z~~~le~4 Dimethylnitrosamine~~ 6-(p-dimethylamiIlc,l,hrnyl:lzo) quifwlined6 AflatosirP (from Br:Ali:tl~ peanut men1 i

(DAH)

administered ipg/tlay )

Days fctl

r,O(lO-6000 400 (for .i-dav weeli)

10.5 2 1X-336

3000 6*

X:3

of more importance in so-called underdeveloped regions where the endemic nature associated with consumption of toxic fungal metabolites is continuous and becomes a factor for serious consideration. Another aflatoxin, termed aflatoxin M, not only occurs in crude aflatoxin mixtures but has been isolated in the urine of sheep and has been elaborated in the milk of sheep and cattle (4 2, 43). When cow’s milk is treated with rennet, the casein or cheese curd fraction occludes aflatoxin M or “milk toxin” and this would be true of butter. This would mean that both products, in an area where cows ingested fungal-contaminated feeds, could be implicated in aflatoxicoses. Hence, from an epidemiological viewpoint, where there are focal points of exposure milk and milk products are to be surveyed to ascertain the degree of contamination and exposure of the individuals. In Ethiopia, for example, Coady (48) has made an excellent survey of the porridges and fermented foods, including beverages 01 beers made from fungally contaminated grains. Field evaluations must be pursued in such areas to better delineate the etiology of liver disease and a cause and effect relationship, if any, between these products and liver cancer. It has been suggested that in respect to mycotoxin exposure the transition from a malnutrition state to adequate nutritional status through protein concentrates may indeed be the catalyst for induction of a carcinoma from a precancerous dormant liver (2, 49). There is also a link between pyridoxine deficiency, aflatoxin, and actinomycin D poisoning in some work with baboons (50) which signals particularly in studies in Africa the role that vitamins may play and also the attention that must be given to kwashiorkor (51). Other studies have been conducted with the rhesus monkeys on high and low protein diets with an aflatoxin challenge (52) and these studies showed an aflatoxin-protein level interaction.

FOOD

COKTAMINANTS

AND

LIVER

SEOI’LASIA

239

One should certainly be discouraged from the supposition that primates, and particularly man, may have an immunity to fungal hepatotosins. The site of action of a&toxin or other mycotoxins may not be restricted to the liver, It has been shown by Butler and Barnes (53) that primary adenocarcinomas of the stomach could be induced as well as a renal adenoma in the rodent. Gastric glandular carcinoma in experimental animals is apparently uncommon and difficnIt to induce. However. Oettle (54) was able to routinely produce cancer of th(x glandular stomach in a colons of 3lasto~~~s with an incidence of 31% of the males and 47% of the fern&s. In 1961, Oettle (55 ) reaff?rnled these findings, demonstrating an incidence of 34% in the males and 71X in the females over 18 months of age. Tnmors were observed at other sites (pituitary, adrenals, vagixx, skin, thyroid. breast, and liver ). In 1965, Sncll (56) reported similar hiyh rates of stomach cancer. These findings were unprecedented. Simnlcrs ef (11. ( 57). in feeding ;L diet free of nflatosin, were unable to duplicate the findings of Oettlc and Snell. indicating that an original diet used by these in\zestigators must have been contnminatc~d with &toxin. The components in the diet which were contaminated \\‘cre peanut meal and maize meal. .\lost cases with primtry hepatoma have had an antcccdent of cirrhosis and this association appears higher among the Africans than the Caucasians (58, 59). It is of further interest that t\tro-thirds of the hepatolnas reported in the US,4 have extra-hepatic metastasis and 60% have cirrhosis preceding the hepatomas; while children with primary hepatoma do not visually have cirrhosis. according to Burdcttca ( 60). Hutkr (61 ) in his discussion of liver ininry and &toxin states that human primary liver carcinoma is mainly a disease of young people living in tropical and semitropical countrks. whereas the incidence in North Anwricn and Elux)pe is hy comparison rare. The global distribution of primary hepatoma is such that the higher incidence of the disease is in the sub-Sahara region of Africa. Sontheast Asia, Japan, and southern India. The highest incidence rate appears to he in Mozambique, VSwctling that in the llnited States about 500 times. These facts seem to point prcdominantlv to an environmental factor rather than genetic. In this connection, Oettle (62) maintained that at least 80% of the cancers affecting western man are attrihutahle to his rnamic’r of life and hence arc potentially preventable. This vicn- is held by others, too, although definitive data which support such a declaration are not yet at hand. llost of this discussion has dealt with the problem of the aflatosins. There are other tosins proclllcecl by the Peni~‘illiz~~n genus which have equally significant hepatotosic and hep”tocarcinoSenic effects. One member of the Penicillium species. P. griseofuloin, appears to be tumorigenic and cocarcinogenic. The antibiotic griseofulvin, when fed to mice at level of O.%l.O% in the diet, produced li\,cr hypertrophy, bili:lry cirrhosis, and hepatomas ( 63 ). -4 summation of some of the mycotouins and plant products which occur naturally and are involved in carcinogenic response in various experimental animals is given in Tables 17 and \‘I. Some speculation as to their etiology in diseases of man has been made hut extensive epidemiological studies are required at least to delineate their involvement in human neoplasia.

240

H.

F. KR/kYBILL

TABLE (~.4RclNOGESIC

SaTuRar,

PRODUCTS

AND

V

GASTR~INTEWJ~AL

Chemical

compolmd

I~uteosk~lill Cl-conlalnilrg

Species ohserved ..__~~~~~_...

peptidr

(;riseofidvill ?ifiiltoxirl

(,a, ~XIYC~TOXINS

NEOPLASIA:

I{,

Target

Rats Mire

Liver

Mice

Live]

Trout

Liver St,omadl

Ducklings ILlts C,uinr:i pig il. versicolor

StcrigmatocystilI III.

El’IDEMIOLOGY

OF

Rats

GASTROINTESTINAL

organ

~~

IJive CARCINOGENS

Data from studies on experimental animals, within the last decade, have provided a fuller comprehension of the potential role of food contaminants in human gastrointestinal carcinogenesis. In the preceding discussion, a wide spectrum of these natural product tumorigens and carcinogens have been described. Many of these compounds have been isolated, their chemical structures determined and synthesized in the laboratory for ultimate bioassay. Further studies on nonhuman primates have provided inferentially their possible association to induction of neoplastic disease in man. Furthermore, epidemiological surveys in such regions as Southeast Asia, India, Japan, and Africa have contributed important presumptive evidence for follow-up studies. In most of these investigations the data relates mostly to the two important target organs, the liver and the stomach. In a search for exogenous factors that might influence the geographic distribution of stomach cancer patients, Haenszel (64) TABLE CARCINOGENIC

NATURAL

PRODUCTS

AKD

Natural product food contaminant Senecio (Crotolaria, (Bush Tea) Cycad

Heliotrope)

Oil of sassafras

Bracken Seleniferous

Chemical compound

grains

or forages

(h)

NEOPLASM:

PLANT

Species observed

PRODUCTS

Target organ

Rat

Liver

Rat

Jiver

Safrole (p-allylmethylenedioxybenzene) Dihydrosafrole

Rat

Liver

Rat

Esophagus

Not

Rat

Small

Rat

Liver

Pyrrolizidine Cycasin

nuts

VI

~;ASTROINTESTIKAL

alkaloids (methylaeoximethane)

identified

Selenomethionine Selenocystine Selenide Selenate

in&tine

FOOD

CONTAMINANTS

AND

LIVER

241

NEOPLASIA

has indicated that dietary factors are the most obvious. In a consideration of dietary effects the following categories are ielevant: (a) Naturally occurring carcinogens in a food; (b) a carcinogen produced by elevated temperatures, i.e.. processing and/or pyrolysis of food components (carbohydrates and fats); (c) the absence of protective factors such as observed in protein malnutrition or kwashiorkor; and (d) production of carcinogens through microbial or fungal invasion of stored food products. There are certain key findings to date which supplement the above information and offer a basis for better delineation of epidemiological studies. For example, these are- as follows in the case of human gastric carcinoma: (a) Low incidence of this disease in the United States as contrasted with rates for foreign-born groups which exceed those for native born populations. Dungal (10) has drawn attention to the incidence of stomach cancer among the Icelanders as compared with similar ethnic groups either in the United States or othef countries. Similarly, another illustration is afforded by comparison of the incidence of primary hepatomas in the Chinese as dependent upon place of birth and previous environment (Table VII ) ; (b ) an indication of the TABLE INFLUENCE OF PLACE OF BIRTH ON THE INCIDENCE OF PRIM.ZRY

VII* AND PREVIOUS EWIRONXENT HEPATOUAS IN THE CHINESE Origin

Born

of birth Migrated

in Singapore

from

China

Percent of total

Total number Chinese in Singapore (1947) Consecut,ive admissions to medical Primary hepatomu * Adapted

from

Shanmugaratnam

wards

421,406 341

57.7 5.5.4 15

1 (65 and 66),

(1956

and

Total number 281,032 43% 6X

Percent of total 38 5 44.6 $8 .5

1961).

role of environmental factors demonstrated by variation in gastric cancer rates among countries in different latitudes; (c) declining rate of stomach cancer in the United States which is not so evident in other’ countries, especially the less developed nations; and (d) the apparent higher incidence of gastric cancer in northern latitude countries which transcends even north-south differences in the United States. Pursuing these leads in incidence of gastric carcinoma with respect to ethnic group and geographic variation presupposes an accurate accounting of national dietaiy histories. In most cases, such information on specific food items consumed is not available since reporting has been on the basis of general classification such as meats, fruits, cereal products, or vegetables. The etiology of the disease in question may be dependent upon one or two foods which, because of incident contamination, contribute predominantly to continuous exposure and ultimate production of a cancerous lesion. Therefore, more recent investigations are focusing on the acquisition of qualitative and quantitative data on specific foods consumed in these regions by various ethnic groups. Haenszel (64) has stressed

242

H.

F. KRAYBILL

the fact that previous retrospective studies have been h~&capped by Ia& of serious efforts to collect dietary histories for cancer patients and matched controls in population surveys. Segi (67) and Quisenberry (68) have initiated some efforts in this direction. The significance of providing information on specific foods might be illustrated by the finding of Japanese investigators that there was a higher stomach cancer risk among persons who consume predominantly rice as a staple food as compared with those who supplement rice with other cereal products, and even a lower risk among those Japanese who are heavy users of soybean products. As mentioned previously, yellowed rice or fungally contaminated rice (P. islandicum ) have been implicated in gastrointestinal carcinoma, More recent knowledge on the role of mycotoxins has indicated the importance of considering the degree of contamination of foods rather than seeking an association between the specific food item per se and the disease process. Prior to the acquisition of the current information and data on the presence and concentration of various food contaminants (pesticides, radionuclides, mycotoxins, plant and seed toxicants, and processing degradation products, etc.), assumptions were made that specific foods in a diet as, for example, certain fruits or vegetables, may be implicated in higher rates of cancer of specific population groups compared to matched controls where diet composition was different. Haenszel (64)) for example, makes certain speculations about stomach cancer incidence in terms of where trends are toward higher consumption of citrus fruits for lower stomach cancer rate vs. higher rates in northern latitude where apples are consumed. With reference to vegetables, for example, he states that a major discrepancy in relating the use of lettuce and cabbage to the distribution of stomach cancer is the greater use of cabbage in areas where stomach cancer may be higher as compared to those areas of lower incidence in which lettuce is prealthough a relationship may be dominant. Such an association seems spurious, sought. It would appear more reasonable to search for a source or sources of food contaminants that may be associated with a higher incidence of gastric carcinoma. In view of our current knowledge on this subject, a series of controlled retrospective studies of food and diet of liver and stomach cancer patients may offer possibilities which can now be exploited. A possible etiological relationship between mycotoxins and hepatomas in the South African Bantu has been proposed (4, 62, 69). The fully developed hypothesis has been advanced to the extent that it is claimed that hepatomas are more common in the Bantu from Mozambique since temperature and humidity are high, more optimal for fungal growth; as contrasted to the lower incidence in the and humidity are less conducive Bantu around Johannesbur,, 0 where temperature for fungal growth. Whereas there is rather strong evidence pointing toward an association between a&toxin and primary hepatoma in Africans of the subSahara regions, one cannot discount the fact that other carcinogenic mold metabolites as well as viruses and carcinogens of plant origin might also be implicated and local variations of this plant in the etiology of the disease. Sefzecio alkaloids are used as food, snuff, and herbal medicines in the Tianskei (70) and consequently could be contributors to the etiology of liver cancer. TE S--.+h Africa, the

FOOD

COST.4hIl~ASTS

AND

LIVEH

SEOPLASIA

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National Nutrition Research Institute is concerned \vith stlldies on mycotosins as etiologic agents in malignwt hepatomas in the lsantu. Since the toxic fungal metalwlites have been shown to be rc*sponsible for a di\.rrsity of disease syndromes in animals and man and are now heavily implicated in the etiology of human carcinogenesis. it is essential that preventive measures should be imposed. There are three ways in which action of mycotoxins may lx prevented: (1) Prevention of fungal growth; (2) clestruction of the toxic fungal mctabolite after elaboration; and (3) addition of a component to the food or feed to counteract the toxic fungal metabolite when it is ingested. In this last category it is proposed that dietary supplementation with sulfhydryl-containing :Imino acids such as cysteine or glutathione might react with the reactive lactone group on aflatoxin and thus bring about its detoxification in the liver. In cifm studies, for example. have shown that the high reactive P-propiolactone, a carcinogenic material, would combine with the sulfhydryl group in neutral aqueous solution nnd the purified crystallin material isolated lost most of its carcinogenic activity (71). Epidemiological studies on chemical carcinogcnesis originating in food and diet of man have been somewhat limited in contrast with investigations of cancer mediated through the more readily identifiable causc~and effect relationships as, for example, elicited in occupational exposures. Studies relating to liver and stomach cancer in human populations in widely distributed geographic arcw have been restricted due to difficulties encountered in establishment of a series of controlled retrospective or prospective studies. The variables encountered in such a study and the lack of adequate data on dietary intakes have thwarted progress. The field of inquiry can now lx narrowed and many of the variables controlled \vith supporting data from animal studies. The collection of data in controlled studies on man, such as those now underwav in South Africa and India, mav resolve some apparent inconsistencies in the crude information currentlv available. It is anticipated that such studies will lead to the elucidation of a single agent in food or a combination of agents induced through environmental conditions, all of \vhich will fit into the total epidemiologic pattern for cancer at specific locations in the Rastrointestinal tract. The findings thus attained can be corroborated 1)) other means such as observations on defined cohorts exposed to specific and similar stressesor further substantiation may be afforded throllgh the development of csperimental biological response situations LS olwerved in the population groups that nray be under study. The most promisin,(7 area of endeavor is the investigation of the action of afiatosins in man. Prospc&ve and retrospective studies. incorporating clinical findings, shollld serve to provide the necessary epidemiological data concerning the role of these mycotoxins in thca etiology of Sastroiiitestinal cancer. LArecent report from India has provided useful information in this direction (72). This stlldy demonstrated that a significant portion of breast milk samples from mothers of cirrhotic children contained aflatoxin H,. Xloreover urine samples from these cirrhotic children showed the presence of this mycotouin. This type of baseline

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evidence provides a background for follow-up studies that may demonstrate impotitant cause and effect relationships. REFERENCES 1. TANNENBAUM, A. (1959). Nutrition and Cancer. In “The physiopathology of Cancer” (F. Hornburger, ed.) pp. 517-562. Harper (Hoeber), New York. 2. KRAYBILL, H. F. ( 1963). Carcinogenesis Associated With Foods, Food Additives, Food Degradation Products and Related Dietary Products. J. Clin. Pharmacol. Therapeutics 4, 73-87. 3. CARTER, H. E., CANNON, P. R., KENSLER, C. J., LEVIN, M. L., MILLER, J, A., NELSON, A. A., AND SHUBIK, P. ( 1961). P ro bl ems in the Evaluation of Carcinogenic Hazard from Use of Food Additives. Cancer Res. 21, 429. 4. KRAYBILL, H. F., AND SHIMKIN, M. B. (1964). C arcinogenesis Related to Foods Contaminated by Processing and Fungal Metabolites. A&an. Cancer Res. 8, 191-248. 5. MILLER, J. A. (1966). Tumorigenic and Carcinogenic Natural Products. In “Toxicants Occurring Naturally in Foods,” NAS-NCR Publication 1354, Washington, D. C. 24-39. 6. BAILEY, E. J., AND DUNGAL, N. ( 1958). Polycyclic hydrocarbons in Icelandic Smoked Food. Bait. J. Cancer 12, 348-350. 7. LIJINSKI’, W., AND SHUBIK, P. (1964). Benzo( a )pyrene and Polynuclear Hydrocarbons in Charcoal Broiled Meat. Science 145, 53-55. 8. HUEPER, W. C., AND PAYNE, W. W. (1960). C arcinogenic Studies on Soot of Coffee Roasting Plants. AMA Arch. of Pathol. 69, 716-727. 9. KURATSUNE, M., AND HUEPER, W. G. ( 1960). Polycyclic Aromatic Hydrocarbons in Roasted Coffee. J. Natl. Cancer Iwt. 24, 463469. 10. DUNGAL, N. ( 1961). The Special Problem of Stomach Cancer in Iceland. J. Am. Med Assoc. 176, 789-798. 11. Adaisory Committee to Surgeon Gened of Public Health Service Report (1964). “Smoking and Health,” P&Z. No. 1103, G. P. O., Washington D. C. 12. VOITELOVICH, E. A., DIKUN, P. P., DYMARSIUI, J. V., AND SHABAD, L. M. ( 1957). A Comparative Study of the Incidence of Malignant Tumors in the Tukun District of the Latvian SSR. Probl. Oncology 3, 351-356. 13. FITZHIJGH, 0. G. ( 1951). A Comparison of the Chronic Toxicities of the Synthetic Sweetening Agents. J. Am. Pharm. Assoc. 11, 583-586. 14. STEYN, D. G. ( 1953-54). The Processing of Food and the Contamination of Food and Beverages by Chemicals. Lantern 2, No. 4 and 3, No. 1, 2, 3. 15. LOXG, E. L., NELSOY, A. A., FITZHUGII, 0. G., AND HANSEN, W. H. ( 1963 ). Liver Tumors Produced in Rats by Feeding Safrole. Arch. Pathol. 75, 595-604. 16. HOMHUHGEH, F., KELLEY, T., FRIEDLER, G., AND RUSSFIELD, A. B. ( 1961). Toxic and Possible Carcinogenic Effects of 4-Allyl-1, 2-Methylenedioxybenzene (Safrole) in Rats on Deficient Diets. Med. Exper. 4, l-11. 17. OSER, B. L., AND OSER, M. ( 1960). 2- ( p-tert-Butylphenoxy ) isopropyl 2-chloroethyl Sulfite (Aramite). Toxicol. Appl. Pharmacol. 2, 441-457. 18. STERNBERG, S. S., PUPPER, H., OSEII, B. L., AND OSER, M. (1960). Gallbladder and Bile Duct Adenocarcinomas in Dogs After Long Term Feeding of Aramite. Cancer 13, 780-789. 19. FITZHUCH, 0. G., AXD NELSON, A. A. ( 1948). Liver Tumors in Rats Fed Thiourea and Thioacetamide. Science 108, 626-628. 20. HODGE, H. C., BOYCE, A. M., DEICHMANN, W. B., AND KEUYBILL, H. F. (1967). Toxicology and No Effect Levels of Aldrin and Dieldrin. Toxicol. Appl. Pharmacol. 10, 613675. 21. KOBAYASHI, A., AND h’IATSUMOT0, H. (1965). Studies on Methylazoxymethanol the Aglycone of Cycasin. Arch. Biochem. Biophys. 110, 373-380. 22. MATSUMOTO, H., NOGAHAME, T., AND LARSON, H. 0. (1965). Studies on Methylazoxymethanol, The Aglycone of Cycasin: A Synthesis of Methylazoxymethyl Acetate. Biochem. J. 95, 136.