- Email: [email protected]
Inhibitory effect of chlorogenic acid on methylazoxymethanol acetate-induced carcinogenesis in large intestine and liver of hamsters
Cancer
Letters,
30 (1986)
49
49-54
Elsevier Scientific Publishers Ireland Ltd.
INHIBITORY EFFECT OF CHLOROGENIC ACID ON METHYLAZOXYMETHANOL ACETATE-INDUCED CARCINOGENESIS IN LARGE INTESTINE AND LIVER OF HAMSTERS
HIDEKI MORI*, TAKUJI TANAKA, MASAYOSHI TAKAHASHI Department of Pathology, City 500 (Japan)
Gifu
HIROTO SHIMA, TOKURO KUNIYASU
University
&hoof
of Medicine,
40 Tsukasa-machi,
and Gifu
(Received 11 September 1985) (Revised version received 8 November 1985) (Accepted 26 November 1985)
SUMMARY
The effect of dietary chlorogenic acid on methylazoxymethanol (MAM) acetate-induced carcinogenesis was examined in Syrian golden hamsters. The combined incidence of total large intestinal tumors from male and female hamsters, and the combined incidence of large intestinal adenocarcinemas or the incidence of the carcinomas of male or female animals of the group given a single intravenous injection of MAM acetate (20 mg/kg body wt) and then fed the diet containing 0.025% chlorogenic acid for 24 weeks were significantly lower than those of hamsters given MAM acetate alone. The numbers of hyperplastic liver cell foci in male and female hamsters given MAM acetate and chlorogenic acid were also significantly smaller than those of hamsters given MAM acetate alone. These results indicate an inhibitory effect of chlorogenic acid on MAM acetate-induced carcinogenesis in hamsters.
INTRODUCTION
Chlorogenic acid is a phenolic compound which is widely distributed as a plant constituent [ 111. This phenylpropanoid has been known to have antioxidative effects [6] and to be a potent inhibitor of many enzyme activities [1,3] . Its biological and toxicological properties in animals are not well known. Recently, some genotoxic effects of the chemical were clarified [15]. However, it has also turned out to exert an antimutagenic
*To whom correspondence
and requests for reprints should be addressed.
0304-3835/86/$03.50 0 1986 Elsevier Scientific Publishers Ireland Ltd. Published and Printed in Ireland
50
activity [14] and to show a protective effect on chemical carcinogenesis in mice [7]. On the other hand, possible cocarcinogenic effect of this compound has been suggested [2], since it catalyses N-nitrosamine formation [2,8]. In fact, we have previously reported some enhancing effects of coffee, which is known to contain much of chlorogenic acid, on carcinogenesis induced by N-2fluorenylacetamide or cycasin [5,10]. Since relatively large quantities of this chemical are consumed by the human population in many food items, it is important to determine the properties of the chemical, particularly relating to carcinogenesis. In the present study, the effect of chlorogenic acid on MAM acetateinduced carcinogenesis was examined by its long-term oral administration. MATERIALS
AND METHODS
A total of 98 Syrian golden hamsters (Japan Clea Inc., Tokyo, Japan) of both sexes, 2 months old, were divided into 4 groups. Group I: 12 male and 12 female hamsters were given a single intravenous injection of MAM acetate (Ash Stevens, Milwaukee, WI, U.S.A.) in a dose of 20 mg/kg body wt. The injection was performed at the left subclavian vein under light ether anesthesia at 0900-1000 h. After the injection, animals were kept on a basal diet CE-2 (Japan Clea Inc., Tokyo, Japan) for 24 weeks. Group II: 12 males and 12 females were given the single administration of MAM acetate and given the basal diet mixed with chlorogenic acid (Sigma Chem. Co., St. Louis, MO,.U.S.A.) at a level of 0.025% for 24 weeks. Group III: 10 male and 10 female hamsters were given the diet containing chlorogenic acid for 24 weeks. They did not receive MAM acetate injection. Group IV: 15 males and 15 females were fed the basal diet without chlorogenic acid throughout the experiment (24 weeks) and served as controls. Animals were maintained in the holding room controlled at 20 f 2°C temperature and 50 + 10% relative humidity. A 12-h lightdark cycle was maintained. On termination of the experiment (24 weeks after the start of the experiment) all animals were killed and autopsied. At autopsy, the gastrointestinal tract was removed. A longitudinal incision was made from the stomach to the rectum and tissue was rinsed in physiological saline, spread mucosal side upon the filter paper and inspected for lesions. The number, position, and size of grossly visible tumors in the gastrointestinal tract were noted. The entire intestinal tract was cut into anatomical segments, and rolled in order to present the greatest possible length on one microscopic slide. All tissues including liver and gross lesions were fixed in 10% buffered formalin, sectioned, stained with hematoxylin and eosin, and examined histologically according to the criteria described by Emminger and Mohr [4] for colon neoplasms and those described by Stewart et al. [13] for liver lesions. The areas of the liver sections were calculated with a Dig&rammer Model G (Mutoh Inc., Tokyo, Japan).
30(15/15)
0
0
0
3(3): 2(2)/1(l)
3b (3): 2(2)/l(l)
0
6(7): 4(5)/2(2)
lO(17): 6(9)/4(B)
Adenoma
test (bp < 0.00725,
0
0
OC Od/Od
8(10): 4(4)/4(6)
Adenocarcinema
cP < 0.00071
0
0
0
2(1/l)
Hemangioma
and dp < 0.02873).
0
0
0
0
3(0/3)
4(2/2)
Bile duct adenoma
with liver tumors
0
1(0/l)
Liver cell adenoma
IN EACH GROUP
Total
OF HAMSTERS No. of animals (male/female)
AND LIVER
No. of animals with large intestinal tumors (no. of tumors): male/female
INTESTINE
Y?urvived until the termination of the experiment (24 weeks). b-dSignificantly different from Group I by Fisher’s exact probability
IV (No treatment)
20(10/10)
III (Chlorogenic alone)
acid
24(12/12)
alone)
II (MAM acetate + chlorogenic acid)
20(10/10)
No. of effective animals (male/ female)a
Group (treatment)
:M AM acetate
OF THE LARGE
TUMOR INCIDENCES
TABLE 1
52 RESULTS
The results obtained in the present study are summarized in Tables 1 and 2. In Group I given only MAM acetate, 20 hamsters (10 males and 10 females) survived until the termination of the experiment. Macroscopitally, of these, 10 animals (6 males and 4 females) developed a total of 17 grossly visible tumors in the large intestine (Table 1). They were sessile or polypoid. One female had a small intestinal tumor. Histologically, tumors in the large intestine were adenomas or adenocarcinomas. A small intestinal tumor was diagnosed as adenocarcinoma. One hamster (female), 4 hamsters (2 males and 2 females) and 2 hamsters (1 male and 1 female) had a liver cell adenoma, bile duct adenomas and hemangiomas, respectively. In group II administered MAM acetate and chlorogenic acid, all animals (12 males and 12 females) survived until the termination of the experiment. Of these 3 hamsters (2 males and 1 female) developed 3 tumors in the large intestine (Table 1). Histopathologically, these neopiasms were all adenomas. Bile duct adenomas were obtained in 3 females. There were no small intestinal neoplasms in Group II. The neoplasms of the large intestine in Groups I and II were mainly seen in the cecum or the upper two-thirds of the colon. Besides the liver neoplasms, focal hyperplastic liver cell lesions (altered liver cell foci) were frequently observed in animals of both groups. The foci were mainly composed of eosinophilic or basophilic cells (Table 2).
TABLE 2 NUMBER OF ALTERED LIVER CELL FOCI IN HAMSTERS GIVEN MAM ACETATE ALONE OR MAM ACETATE WITH CHLOROGENIC ACID Group (treatment) I I (MAM acetate alone)
II (MAM acetate + chlorogenic acid)
No. of hamsters examineda
Total no. of liver cell foci and each cell typeb
M 10
282
F 10
285
M 11
110
F 11
138
E 182 C 18 B 82 El95 iC 6 B 84 ( E 74 C 6 B 30 E 97 (C 6 B 35
No. of foci/cm2
10.0 r 3.8c
11.2 k 4.7
*M = male; F = female. bE = eosinophilic cell foci; C = clear cell foci; B = basophilic cell foci. CMean t SD. dSignificantly different from Group I by Student’s t-test (P < 0.01).
5.3 f 2.3d 6.4 2 3.0d
53
All animals in Group III fed the chlorogenic acid containing diet alone or Group IV (non-treated controls) survived u,ntil the termination of the experiment. However, no neoplasias or hyperplastic lesions were seen in any animals of these groups (Table 1). Statistically, the combined incidence of total intestinal neoplasias from male and female hamsters of Group II was significantly lower than that of Group I (P < 0.00725). The combined incidence of large intestinal adenocarcinomas in males and females and the incidence of the carcinomas of males or females of Group II were also significantly lower than those of Group I (P< 0.00071, P< 0.02873 and P< 0.02873) (Table 1). The numbers of altered hepatocellular foci/cm2 in males and females of Group II were also significantly smaller than those of Group I (P< 0.01and P < 0.01) (Table 2). No significant differences in the incidences of liver neoplasms (liver cell adenomas, bile duct adenomas or hemangiomas) between Groups I and II were noted. DISCUSSION
In the present study, the incidences of large intestinal neoplasms and hyperplastic liver cell lesions of hamsters given MAM acetate and chlorogenie acid were significantly lower than those of hamsters administered MAM acetate alone. These results indicate an inhibitory effect of chlorogenie acid on MAM acetate-induced colon and liver carcinogenesis. In the present experiment, both the incidence and multiplicity of intestinal tumors in animals given MAM acetate were rather low. This is probably due to the shorter duration of the experiment. The morphology of the altered liver cell foci observed in the present study resembled that in rats [13] and they are also considered to be preneoplastic lesions for hepatocellular neoplasms. Similar small lesions of hamsters have recently been described by Stenback et al. [12] and Moore et al. [9]. Present results indicating the inhibitory effect of chlorogenic acid on MAM acetate-induced carcinogenesis in the hamster model appear to support the report by Lasca [7] showing its protective effect on benzo[a] pyreneinduced tumorigenesis in mice. Stich et al. [15] reported some genotoxic activities like convertogenic or clastogenic effects of this chemical. They also reported that chlorogenic acid is not mutagenic in Salmonella mutagenesis test [ 151 and that it inhibits mutagenicity of the nitrosation products of methylurea [14]. Challis and Bartlett [ 21 and Lathia and Frentzen [8] reported catalytic effect of chlorogenic acid on formation of carcinogenic nitrosamine. In the present study, neither neoplastic nor preneoplasbic changes were observed in hamsters given chlorogenic acid alone for 24 weeks. This may suggest that the chemical has no clear carcinogenic potency, although the duration of the present experiment is not long enough. Previously, we reported some enhancing effects of coffee on the development of cola-rectal adenomas in SD rats by cycasin [lo] or mammary tumorigenesis in SD rats by N-2-fluorenylacetamide [5]. The present experiment also
suggests that these effects of coffee may be caused by other constituents in coffee. Further studies to confirm the modifying effect of chlorogenic acid on chemical carcinogenesis are being carried out. REFERENCES
5
9
10 11 12
13 34
15
Albergbina, F.A.M. (1964) Enzyme inhibition by oxidized chlorogenic acid. Life Sci., 3,49-54. Challis, B.C. and Bartlett, C.D. (1975) Possible cocarcinogenic effects of coffee constituents. Nature, 254, 532-533. Das, M., Bickers, D.R. and Mukhtar, H. (1984) Plant phenols as in vitro inhibitors of glutathione S-transferase(s). Biochem. Biophys. Res. Commun., 127, 427-433. Emminger, A. and Mohr, U. (1982) Tumours of the oral cavity, cheek pouch, salivary glands, oesophagus, stomach and intestines. In: Pathology of Tumours in Laboratory Animals, Vol. III: Tumours of the Hamster, pp. 45-68. Editor:.V.S. Turusov. IARC, Lyon. Fujii, M., Mori, H., Nishikawa, A. and Takahashi, M. (1980) Effect of coffee on carcinogenicity of N-2-fluorentylacetamide. Acta Sch. Med. Univ. Gifu, 28, 295298. Hayase, F. and Kato, H. (1984) Antioxidative compounds of sweet potatoes. J. Nutr. Sci. Vitaminol., 30, 37-46. Lasca, P. (1983) Protective effects of ellagic acid and other plant phenols on benzo(a)pyrene-induced neoplasia in mice. Carcinogenesis, 4, 1651-1653. Lathia, A. and Frentzen, U. (1980) Synergic effect of chlorogenic acid and thiocyanate on in vitro formation of N-methyl-N-nitrosoaniline under physiological conditions. Food Cosmet. Toxicol., 18, 463-465. Moore, M.A., Satoh, K., Kitahara, A., Sato, K. and Ito, N. (1985) A protein crossreacting immunohistochemically with rat glutathione S-transferase placental form as a marker for preneoplasia in Syrian hamster pancreatic and hepatocarcinogenesis. Jpn. J. Cancer Res. (Gann), 76,1-4. Mori, H. and Hirono, I. (1977) Effect of coffee on carcinogenicity of cycasin. Br. J. Cancer, 35,369-371. Sondenheimer, E. (1964) Chlorogenic acids and related depsides. Bot. Rev., 30, 677-712. Stenback, F., Mori, H., Furuya, K. and Williams,G.M.(1986) The pathogenesis of dimethylnitrosamine-induced hepatocellular cancer in hamster liver and a lack of enhancement by phenobarbital. J. Natl. Cancer Inst., in press. Stewart, H.L., Williams, G.M., Keysser, C.H., Lombard, L.S. and Montali, R.J. (1980) Histologic typing of liver tumors of the rat. J. Natl. Cancer Inst., 64, 177-206. Stich, H.F., Rosin, M.P. and Bryson, L. (1982) Inhibition of mutagenicity of a model nitrosation reaction by naturally occurring phenolics, coffee and tea. Mutat. Res., 95,119-128. Stich, H.F., Rosin, M.P., Wu, C.H. and Powrie, W.D. (1981) A comparative genotoxicity study of chlorogenic acid (3-0-caffeloquinic acid). Mutat. Res., 90, 201212.
Letters,
30 (1986)
49
49-54
Elsevier Scientific Publishers Ireland Ltd.
INHIBITORY EFFECT OF CHLOROGENIC ACID ON METHYLAZOXYMETHANOL ACETATE-INDUCED CARCINOGENESIS IN LARGE INTESTINE AND LIVER OF HAMSTERS
HIDEKI MORI*, TAKUJI TANAKA, MASAYOSHI TAKAHASHI Department of Pathology, City 500 (Japan)
Gifu
HIROTO SHIMA, TOKURO KUNIYASU
University
&hoof
of Medicine,
40 Tsukasa-machi,
and Gifu
(Received 11 September 1985) (Revised version received 8 November 1985) (Accepted 26 November 1985)
SUMMARY
The effect of dietary chlorogenic acid on methylazoxymethanol (MAM) acetate-induced carcinogenesis was examined in Syrian golden hamsters. The combined incidence of total large intestinal tumors from male and female hamsters, and the combined incidence of large intestinal adenocarcinemas or the incidence of the carcinomas of male or female animals of the group given a single intravenous injection of MAM acetate (20 mg/kg body wt) and then fed the diet containing 0.025% chlorogenic acid for 24 weeks were significantly lower than those of hamsters given MAM acetate alone. The numbers of hyperplastic liver cell foci in male and female hamsters given MAM acetate and chlorogenic acid were also significantly smaller than those of hamsters given MAM acetate alone. These results indicate an inhibitory effect of chlorogenic acid on MAM acetate-induced carcinogenesis in hamsters.
INTRODUCTION
Chlorogenic acid is a phenolic compound which is widely distributed as a plant constituent [ 111. This phenylpropanoid has been known to have antioxidative effects [6] and to be a potent inhibitor of many enzyme activities [1,3] . Its biological and toxicological properties in animals are not well known. Recently, some genotoxic effects of the chemical were clarified [15]. However, it has also turned out to exert an antimutagenic
*To whom correspondence
and requests for reprints should be addressed.
0304-3835/86/$03.50 0 1986 Elsevier Scientific Publishers Ireland Ltd. Published and Printed in Ireland
50
activity [14] and to show a protective effect on chemical carcinogenesis in mice [7]. On the other hand, possible cocarcinogenic effect of this compound has been suggested [2], since it catalyses N-nitrosamine formation [2,8]. In fact, we have previously reported some enhancing effects of coffee, which is known to contain much of chlorogenic acid, on carcinogenesis induced by N-2fluorenylacetamide or cycasin [5,10]. Since relatively large quantities of this chemical are consumed by the human population in many food items, it is important to determine the properties of the chemical, particularly relating to carcinogenesis. In the present study, the effect of chlorogenic acid on MAM acetateinduced carcinogenesis was examined by its long-term oral administration. MATERIALS
AND METHODS
A total of 98 Syrian golden hamsters (Japan Clea Inc., Tokyo, Japan) of both sexes, 2 months old, were divided into 4 groups. Group I: 12 male and 12 female hamsters were given a single intravenous injection of MAM acetate (Ash Stevens, Milwaukee, WI, U.S.A.) in a dose of 20 mg/kg body wt. The injection was performed at the left subclavian vein under light ether anesthesia at 0900-1000 h. After the injection, animals were kept on a basal diet CE-2 (Japan Clea Inc., Tokyo, Japan) for 24 weeks. Group II: 12 males and 12 females were given the single administration of MAM acetate and given the basal diet mixed with chlorogenic acid (Sigma Chem. Co., St. Louis, MO,.U.S.A.) at a level of 0.025% for 24 weeks. Group III: 10 male and 10 female hamsters were given the diet containing chlorogenic acid for 24 weeks. They did not receive MAM acetate injection. Group IV: 15 males and 15 females were fed the basal diet without chlorogenic acid throughout the experiment (24 weeks) and served as controls. Animals were maintained in the holding room controlled at 20 f 2°C temperature and 50 + 10% relative humidity. A 12-h lightdark cycle was maintained. On termination of the experiment (24 weeks after the start of the experiment) all animals were killed and autopsied. At autopsy, the gastrointestinal tract was removed. A longitudinal incision was made from the stomach to the rectum and tissue was rinsed in physiological saline, spread mucosal side upon the filter paper and inspected for lesions. The number, position, and size of grossly visible tumors in the gastrointestinal tract were noted. The entire intestinal tract was cut into anatomical segments, and rolled in order to present the greatest possible length on one microscopic slide. All tissues including liver and gross lesions were fixed in 10% buffered formalin, sectioned, stained with hematoxylin and eosin, and examined histologically according to the criteria described by Emminger and Mohr [4] for colon neoplasms and those described by Stewart et al. [13] for liver lesions. The areas of the liver sections were calculated with a Dig&rammer Model G (Mutoh Inc., Tokyo, Japan).
30(15/15)
0
0
0
3(3): 2(2)/1(l)
3b (3): 2(2)/l(l)
0
6(7): 4(5)/2(2)
lO(17): 6(9)/4(B)
Adenoma
test (bp < 0.00725,
0
0
OC Od/Od
8(10): 4(4)/4(6)
Adenocarcinema
cP < 0.00071
0
0
0
2(1/l)
Hemangioma
and dp < 0.02873).
0
0
0
0
3(0/3)
4(2/2)
Bile duct adenoma
with liver tumors
0
1(0/l)
Liver cell adenoma
IN EACH GROUP
Total
OF HAMSTERS No. of animals (male/female)
AND LIVER
No. of animals with large intestinal tumors (no. of tumors): male/female
INTESTINE
Y?urvived until the termination of the experiment (24 weeks). b-dSignificantly different from Group I by Fisher’s exact probability
IV (No treatment)
20(10/10)
III (Chlorogenic alone)
acid
24(12/12)
alone)
II (MAM acetate + chlorogenic acid)
20(10/10)
No. of effective animals (male/ female)a
Group (treatment)
:M AM acetate
OF THE LARGE
TUMOR INCIDENCES
TABLE 1
52 RESULTS
The results obtained in the present study are summarized in Tables 1 and 2. In Group I given only MAM acetate, 20 hamsters (10 males and 10 females) survived until the termination of the experiment. Macroscopitally, of these, 10 animals (6 males and 4 females) developed a total of 17 grossly visible tumors in the large intestine (Table 1). They were sessile or polypoid. One female had a small intestinal tumor. Histologically, tumors in the large intestine were adenomas or adenocarcinomas. A small intestinal tumor was diagnosed as adenocarcinoma. One hamster (female), 4 hamsters (2 males and 2 females) and 2 hamsters (1 male and 1 female) had a liver cell adenoma, bile duct adenomas and hemangiomas, respectively. In group II administered MAM acetate and chlorogenic acid, all animals (12 males and 12 females) survived until the termination of the experiment. Of these 3 hamsters (2 males and 1 female) developed 3 tumors in the large intestine (Table 1). Histopathologically, these neopiasms were all adenomas. Bile duct adenomas were obtained in 3 females. There were no small intestinal neoplasms in Group II. The neoplasms of the large intestine in Groups I and II were mainly seen in the cecum or the upper two-thirds of the colon. Besides the liver neoplasms, focal hyperplastic liver cell lesions (altered liver cell foci) were frequently observed in animals of both groups. The foci were mainly composed of eosinophilic or basophilic cells (Table 2).
TABLE 2 NUMBER OF ALTERED LIVER CELL FOCI IN HAMSTERS GIVEN MAM ACETATE ALONE OR MAM ACETATE WITH CHLOROGENIC ACID Group (treatment) I I (MAM acetate alone)
II (MAM acetate + chlorogenic acid)
No. of hamsters examineda
Total no. of liver cell foci and each cell typeb
M 10
282
F 10
285
M 11
110
F 11
138
E 182 C 18 B 82 El95 iC 6 B 84 ( E 74 C 6 B 30 E 97 (C 6 B 35
No. of foci/cm2
10.0 r 3.8c
11.2 k 4.7
*M = male; F = female. bE = eosinophilic cell foci; C = clear cell foci; B = basophilic cell foci. CMean t SD. dSignificantly different from Group I by Student’s t-test (P < 0.01).
5.3 f 2.3d 6.4 2 3.0d
53
All animals in Group III fed the chlorogenic acid containing diet alone or Group IV (non-treated controls) survived u,ntil the termination of the experiment. However, no neoplasias or hyperplastic lesions were seen in any animals of these groups (Table 1). Statistically, the combined incidence of total intestinal neoplasias from male and female hamsters of Group II was significantly lower than that of Group I (P < 0.00725). The combined incidence of large intestinal adenocarcinomas in males and females and the incidence of the carcinomas of males or females of Group II were also significantly lower than those of Group I (P< 0.00071, P< 0.02873 and P< 0.02873) (Table 1). The numbers of altered hepatocellular foci/cm2 in males and females of Group II were also significantly smaller than those of Group I (P< 0.01and P < 0.01) (Table 2). No significant differences in the incidences of liver neoplasms (liver cell adenomas, bile duct adenomas or hemangiomas) between Groups I and II were noted. DISCUSSION
In the present study, the incidences of large intestinal neoplasms and hyperplastic liver cell lesions of hamsters given MAM acetate and chlorogenie acid were significantly lower than those of hamsters administered MAM acetate alone. These results indicate an inhibitory effect of chlorogenie acid on MAM acetate-induced colon and liver carcinogenesis. In the present experiment, both the incidence and multiplicity of intestinal tumors in animals given MAM acetate were rather low. This is probably due to the shorter duration of the experiment. The morphology of the altered liver cell foci observed in the present study resembled that in rats [13] and they are also considered to be preneoplastic lesions for hepatocellular neoplasms. Similar small lesions of hamsters have recently been described by Stenback et al. [12] and Moore et al. [9]. Present results indicating the inhibitory effect of chlorogenic acid on MAM acetate-induced carcinogenesis in the hamster model appear to support the report by Lasca [7] showing its protective effect on benzo[a] pyreneinduced tumorigenesis in mice. Stich et al. [15] reported some genotoxic activities like convertogenic or clastogenic effects of this chemical. They also reported that chlorogenic acid is not mutagenic in Salmonella mutagenesis test [ 151 and that it inhibits mutagenicity of the nitrosation products of methylurea [14]. Challis and Bartlett [ 21 and Lathia and Frentzen [8] reported catalytic effect of chlorogenic acid on formation of carcinogenic nitrosamine. In the present study, neither neoplastic nor preneoplasbic changes were observed in hamsters given chlorogenic acid alone for 24 weeks. This may suggest that the chemical has no clear carcinogenic potency, although the duration of the present experiment is not long enough. Previously, we reported some enhancing effects of coffee on the development of cola-rectal adenomas in SD rats by cycasin [lo] or mammary tumorigenesis in SD rats by N-2-fluorenylacetamide [5]. The present experiment also
suggests that these effects of coffee may be caused by other constituents in coffee. Further studies to confirm the modifying effect of chlorogenic acid on chemical carcinogenesis are being carried out. REFERENCES
5
9
10 11 12
13 34
15
Albergbina, F.A.M. (1964) Enzyme inhibition by oxidized chlorogenic acid. Life Sci., 3,49-54. Challis, B.C. and Bartlett, C.D. (1975) Possible cocarcinogenic effects of coffee constituents. Nature, 254, 532-533. Das, M., Bickers, D.R. and Mukhtar, H. (1984) Plant phenols as in vitro inhibitors of glutathione S-transferase(s). Biochem. Biophys. Res. Commun., 127, 427-433. Emminger, A. and Mohr, U. (1982) Tumours of the oral cavity, cheek pouch, salivary glands, oesophagus, stomach and intestines. In: Pathology of Tumours in Laboratory Animals, Vol. III: Tumours of the Hamster, pp. 45-68. Editor:.V.S. Turusov. IARC, Lyon. Fujii, M., Mori, H., Nishikawa, A. and Takahashi, M. (1980) Effect of coffee on carcinogenicity of N-2-fluorentylacetamide. Acta Sch. Med. Univ. Gifu, 28, 295298. Hayase, F. and Kato, H. (1984) Antioxidative compounds of sweet potatoes. J. Nutr. Sci. Vitaminol., 30, 37-46. Lasca, P. (1983) Protective effects of ellagic acid and other plant phenols on benzo(a)pyrene-induced neoplasia in mice. Carcinogenesis, 4, 1651-1653. Lathia, A. and Frentzen, U. (1980) Synergic effect of chlorogenic acid and thiocyanate on in vitro formation of N-methyl-N-nitrosoaniline under physiological conditions. Food Cosmet. Toxicol., 18, 463-465. Moore, M.A., Satoh, K., Kitahara, A., Sato, K. and Ito, N. (1985) A protein crossreacting immunohistochemically with rat glutathione S-transferase placental form as a marker for preneoplasia in Syrian hamster pancreatic and hepatocarcinogenesis. Jpn. J. Cancer Res. (Gann), 76,1-4. Mori, H. and Hirono, I. (1977) Effect of coffee on carcinogenicity of cycasin. Br. J. Cancer, 35,369-371. Sondenheimer, E. (1964) Chlorogenic acids and related depsides. Bot. Rev., 30, 677-712. Stenback, F., Mori, H., Furuya, K. and Williams,G.M.(1986) The pathogenesis of dimethylnitrosamine-induced hepatocellular cancer in hamster liver and a lack of enhancement by phenobarbital. J. Natl. Cancer Inst., in press. Stewart, H.L., Williams, G.M., Keysser, C.H., Lombard, L.S. and Montali, R.J. (1980) Histologic typing of liver tumors of the rat. J. Natl. Cancer Inst., 64, 177-206. Stich, H.F., Rosin, M.P. and Bryson, L. (1982) Inhibition of mutagenicity of a model nitrosation reaction by naturally occurring phenolics, coffee and tea. Mutat. Res., 95,119-128. Stich, H.F., Rosin, M.P., Wu, C.H. and Powrie, W.D. (1981) A comparative genotoxicity study of chlorogenic acid (3-0-caffeloquinic acid). Mutat. Res., 90, 201212.