High amylose corn starch retarded 7, 12-dimethylbenz[a]anthracene - induced mammary tumor development in female rats

Nubition Research, Vol. 17. No. 6, pp. 103~1046.1997 Copyright 0 1997 Elsevier Science Inc. Printed in the USA. All rights reserved 0271~5317/97 $17.00 + .oo

ELSEVIER

PI1 SO271-5317(97)00067-5

HIGH AMYLOSE

CORN STARCH

RETARDED

7,12-

DIMETHYLBBNZ[a] AN’IHRACBNE - INDUCED MAMMARY DEVELOPMENT IN FEMALE RATS

TUMOR

Seiicbi Kasaoka, MSc, Michiyoshi Ikai, MSc, Akira Oh-hashi, MSc, Tatsuya Morita, PhD, and Shuhachi Kiriyama, PhD *r Azusawa Laboratories, Health Science Laboratories, Yamanouchi Pharmaceutical Co., Ltd. 1-8, Azusawa 1-Chome, Itabashi-ku, Tokyo 174, Japan and *Laboratory of Nutritional Biochemistry, Otsuma Women’s University, Sanbaucho 12, Cbiyoda-ku, Tokyo 102, Japan ABSTRACT The present study was planned to examine the effect of partial replacement corn starch (CS) with high amylose corn starch (HAS) on mammary progression.

of

tumor

The first experiment was to evaluate the effects of HAS on 7,

12-dimethylhenz[a]anthracene

(DMBA)-induced

‘Iwo days after DMBA administration

mammary tumor progression.

(31 mg/kg body weight of rat) at age of

49 days, rats were assigned into 3 groups and fed one of the three experimental diets including

CS, 30% HAS and 13.6% wheat bran (WB), respectively.

The

rats were examined weekly for palpable mammary tumors for 112 days. In the middle of experimental

period, cumulative

bearing rat were significantly

palpable tumors per tumor-

lower in rats fed the HAS and WB diets than in

those fed the CS diet. At autopsy, both mean tumor number and weight per tumor bearing rat were reduced by lo-30%

in rats fed the HAS and WB diets

compared with those in the CS diet, but these differences were not significant. Serum estradiol-17 i3 concentration

did not differ among rats fed the CS,

HAS and WB diets, although fecal excretion of estradiol-17 l3 in rats fed the WB diet was significantly

higher than those in rats fed the CS and HAS diets.

In the second experiment, ileorectostomized

of HAS and CS were compared in

rats. The results showed that only 66% of HAS were digested

in the small intestine, experiment, postprandial suspension

digestibilities

whereas CS was digested up to 99%. blood glucose concentrations

were significantly

intubated CS suspension.

depressed

In the 3rd

in rats intubated HAS

when compared with that in rats

These results suggest that a mild energy restriction

in HAS feeding is effective in prevention of mammary tumor progression. a 1997 astier Science. Inc. Key Words: High amylose corn starch, 7, 12-Dimethylbenz[a]anthracene, Mammary cancer, Energy restriction, Estradiol-17 l3 , ‘Correspondence: Shubacbi Kiriyama, Laboratory of Nutritional Biochemistry, Gtsuma Women’s University, Sanbancho 12, Chiyoda-ku, Tokyo 102, Japan, Telephone:03-5275-6048. 1035

1036

S. KASAOKA et al. INTRODUCI’ION

Epidemiological postmenoposal (1).

data suggest that the incidence

of estrogen-dependent

breast cancer in

women has been well known to be related with obesity and high calorie intake

A number of animal experiments

associated with mammary

also indicated that a high calorie intake was closely

tumorigenesis

12.dimethylbenz[a]anthracene

in rat models induced by the administration

@MBA) (2-4). Kritchevsky

et al. (5) suggested that restriction

of caloric intake was rather responsible for the DMBA-induced than dietary fat content.

mammary tumor development

To reduce the risk of some obese-related

diseases, increased intake of

carbohydrate in the form of dietary fiber and starch has been recommended (6-S). Indeed, epidemiological

of 7,

in Western countries

data suggest that high fiber diet might reduce the breast cancer

risk (9,lO). In addition, animal data clearly show that wheat bran (WB) exerts inhibitory effect on the promotional

phase of mammary

carcinogenesis

in rats, although

it is still remained

unclear whether the main reason is associated with the reduced calorie intake or the reduced serum estrogen (l&12). There is now abundant evidence that some types of starch, so called resistant starch (RS), are not digested in the small intestinal tract, thereby a substantial may reduce the energy density. intestine.

amounts of RS in diet or food

In this regard, RS could behave as dietary fiber in the small

Furthermore, RS offers a major advantage because it can be processed technologically

to alter the apparent fiber content of foods without greatly changing their organoleptic properties. Gur aim of the present study was to experimentally

prove usefulness of increased consumption

of RS for the prevention of mammary tumor progression in rats. In the present study, we used a high amylose corn starch (HAS) as a RS source and compared the inhibitory with WB on DMBA-induced

mammary tumor progression in rats. MATERIALS

Muteriuls.

effects of HAS

AND METHODS

Table 1 shows the chemical composition

of corn starch (CS; Nihon Shokuhin

Kako, Tokyo, Japan), high amylose corn starch (HAS; Hi-maize, Starch Australasia,

Sydney,

Australia) and wheat bran (WB; Nisshin Flour Milling, Tokyo, Japan) used in the present study. Resistant starch content in HAS was defined as the amount of total dietary fiber as determined by AOAC official method (13). Estradiol-17 p and 7, 12.dimethylbenz[a]anthracene

(DMBA)

[2, 4, 6, 7-Q (N)]estradiol-17

B (specific

were purchased from Nacalai Tesque (Kyoto, Japan). activity, 3526 GBq/mmol)

and [l p -‘H (N)]androstendione

(specific activity, 899 GBq/mmol)

were purchased from New England Nuclear (Boston, USA). -6.carboxymethyloxim-bovine

Antiserum

to estradiol-17 i3

serum albumin (immunized animal: rabbit) for radioimmunoassay

was obtained from UCB-Bioproducts present study were of analytical grade.

S.A. (Brussels, Belgium).

All other reagents used in the

1037

STARCH AND MAMMARY TUMOR TABLE 1 Chemical Compositions

of Corn Starch, High Amylose Corn Starch and Wheat Bran * High amylose Corn starch

Ingredients

corn starch

Wheat bran

g/lo(-)g Carbohydrate

85.8

61.5

21.1

Total dietary fiber

ND**

22.6

49.3

13.5

14.1

4.2

Lipids

0.4

1.0

2.1

Protein t

0.3

0.6

16.3

ND **

0.2

7.0

(Resistant starch # ) Moisture

Ash

* Analytical methods were described in MATERIALS AND METHODS. # Resistant starch content in high amylose corn starch was defined here as the amount of total dietary fiber determined by AOAC official method (13). ** Not detected. + N x 6.25.

Gened

treatment of animals.

The study was approved by the Yamanouchi

Pharmaceutical

Co. Animal Use Committee, and animals were maintained in accordance with the guidelines for the care and use of laboratory animals, Yamanouchi of the Sprague-Dawley

Co. Male and female rats

strain (purchased from Shizuoka Laboratory Animal Center, Hamamatsu,

Japan) were used in experiments screen-bottoms

Pharmaceutical

1, 2 and 3.

They were housed in individual

of stainless steel in a room maintained

at 23 2 1 “C and lighted on 0800-2000 h.

Body weight and food intake were recorded daily in the morning before replenishing Tumor induction study (experiment I).

cages with

the diet.

To evaluate the effects of HAS on mammary tumor

progression, 118 female rats (42 days of age) were used in this experiment.

The animals were

acclimatized by the feeding of the standard diet (Table 2). They were allowed free access to diet and water.

At age of 49 days, all rats (average body weight, 166 g; range, 150 - 185 g)

were orally administered of soybean oil.

a single dose of DMBA (31 mg/kg body weight) dissolved in 0.5 mL

1038

S. KASAOKA

Two days after DMBA administration,

et al.

rats were divided into 3 groups on the basis of body

weight. Average body weight at the start of experimental

feeding were 165, 166 and 166 g on a

corn starch (Cs) diet- (n = 43), 30% HAS diet- (n = 36) and 13.6% WB diet-fed groups (n I 39), respectively.

They were allowed free access to the experimental

compositions of experimental diets contained administration,

diets and water.

The

diets are also shown in Table 2. The 30% HAS and 13.6% WB

the same amount of total ,dietary fiber (6.7 g/100 g of diet).

After DMBA

rats were examined weekly for palpable mammary tumors. Feces were collected

for 3 days (day 27-30 after DMBA administration)

to determine the fecal excretions of total bile

acids, neutral sterols and estradiol-17 l3. At day 112 after DMBA administration,

diets were

withdrawn at 10:00 h and blood was collected from the abdominal aorta under anesthesia with diethyl ether between 1200 and 1500 h. determination

After blood collection, aortic serum was used for the

of estradiol-17 l3 . Ovaries were removed rapidly, frozen in liquid N, and stored

at -80°C for the assay of aromatase activity. TABLE 2 Composition of Standard and Experimental Standard

Diets

Experimental

Ingredient

diet *

30% HAS

13.6% WB

g/kg diet Corn starch

535

485

185

349

_

I

300

I

I

_

136

High amylose corn starch Wheat bran Casein

250

250

250

250

Sucrose

100

100

100

100

70

70

70

70

I

50

50

50

Mineral mixture #

35

35

35

35

Vitamin mixture * *

10

10

10

10

Soybean oil Lard

* Diet abbreviations

used: CS, corn starch diet; 30% HAS, 30% high amylose corn starch

diet; 13.6% WB, 13.6% wheat bran diet. # Mineral mixture was prepared according to AIN-93G mineral mixture. from Oriental Yeast Co., Tokyo,

Japan.

* * Vitamin mixture was prepared according to AIN-93G vitamin mixture. from Oriental Yeast Co., Tokyo, Japan. (Wake Pure Chemical Industries, diet, respectively.

It was purchased It was purchased

Choline bitartrate and t-butylhydroquinone

Osaka, Japan) were added 2.5 g/kg and 14 mg/kg of

STARCH AND MAMMARY TUMOR

Serum estradiol-17 B concentration

was measured

according

method of Butcher et al. (14) with a slight modification.

1039 to the radioinmmnoassay

Three milliliters

of serum were

pipetted into 15 mL polyethylene tube for estradiol extraction. Each tube included 47 Bq of [2, 4, 6, 7-3H]estradiol-17 p for correction of procedural losses (74.2 c 0.9% recovery). Extraction of estradiol-17 B was done by 4 times with 2 mL of diethyl ether with vigorous shaking for 2 min. Ether layer was removed, pooled and evaporated into dryness under nitrogen gas. Dried extract was dissolved in 0.1 mL of the mixture of benzene : methanol (85:15, v/v) and placed on Sephadex LH-20 (Pharmacia, Uppsala, Sweden) column. methanol mixture

for 48 h at room temperature

Sephadex, rinsed in the benzene :

and degassed with suction, was filled in a

disposable syringe (inner diameter: 7 mm) up to 2 mL. The column was washed with 5 mL of freshly prepared benzene : methanol mixture. Samples (0.1 mL) were allowed to enter the column. Then, the solvent was added to the column and 2.5 mL of first eluate was discarded. ‘JXvopoint five milliliters of second eluate were collected as estradiol-17 B -containing fraction. After evaporating the solvent under nitrogen gas, 0.15 mL of 0.02 M sodium phosphate buffer @H 7.4) containing 0.5% bovine serum albumin were added to each tube and sonicated for 5 mm to disperse

the precipitates.

radioimmunoassay.

Radioactivity

Thus

resultant

suspension

was used as samples

for

was measured by using a Beckman LS 6000TA scintillation

photometer (Tokyo, Japan). Amounts of estradiol-17 B were expressed as pmol/L serum after correction of procedural losses. In our assay condition, the sensitivity of assay was 6.25 pg of estradiol-17 B , To determine fecal excretion of estradiol-17 S , samples (50 mg of dried and powdered feces) were extracted 4 times with 2 mL of chloroform : methanol (l:l, v/v) mixture at 4°C for 48 h with continuous shaking. Extracts were pooled, and evaporated into dryness under nitrogen stream, The residue was suspended in 4 mL of 30% ethanol with sonication for 10 min. Unconjugated estradiol-17 B was extracted 4 times with 2 mL of diethyl ether. After removing the solvent under nitrogen stream, the residue was dissolved in 0.1 mL of benzene : methanol mixture (85:15, v/v). Estradiol-17 B was separated and measured by the method as described above. Ovarian aroma&se activity was measured according to the method of Thompson and Siiteri (15), quantifying

the amounts of 3HO released from [l B -3H (N)]androstendione.

Specific

activity of aromatase was expressed as pmol tritiated water released from androstenedione per mg protein per min at 37°C. The number of samples from rats fed the CS, HAS and WB diets were 26, 23 and 25, respectively. Protein content was determined by the Kjeldahl method (16). Moisture was determined from the loss in weight after drying at 105°C for 24 h. Ash content was determined by the direct ignitiqn method (525”C, overnight). The content of total dietary fiber was measured by AOAC official method (13). Total lipids were extracted with chlorofornnmethanol (2:l,v/v) by the method of Folch et al. (17) and measured gravimetrically after removing solvent. Carbohydrate content was calculated

by difference,

fiber from total weight. described (18).

Fecal neutral sterols and total bile acids were determined as previously

subtracting

protein, ash, water, lipids and total dietary

S. KASAOKA

et al.

Comparison of digestibility of I-MT and CS in ileorectostomized rats (experiment 2). To evaluate the digestibility

of HAS in the small intestinal tract, we used 8 male rats (35 days

of age). The animals were acclimatized for 7 days by the feeding of the standard diet. At age of 42 days, all rats were subjected

to ileorectostomy.

Rats were deprived of food for 24 h

before surgery, although they had free access to water. They were anesthetized by intraperitoneal injection of Nembutal (sodium pentobarbital50

mg/kg body weight; Abbott Laboratories, North

Chicago, IL). The cecum and colon were surgically removed by the method of Nishimura et al. (18). Rats were not allowed food and water for the first 24 h postoperation, the standard diet for 1 wk.

then they were fed

Thereafter, they were divided into CS diet (n = 4) and HAS diet (n

= 4) groups on the basis of body weight. The HAS diet contained 655 g of HAS as carbohydrate source, 250 g of casein, 50 g of corn oil (Ajinomoto,

Tokyo, Japan), 35 g of mineral mixture

(according to AJN-76 mineral mixture; Oriental Yeast, Tokyo, Japan) and 10 g of vitamin mixture (according to AIN-

vitamin mixture; Oriental Yeast, Tokyo, Japan) per kg diet, The

CS diet contained corn starch in stead of HAS. after feeding experimental

diets).

The feces were collected for 3 days (day 5-7

Starch recovered in the feces was measured by using a Total

Starch Assay Kit (Megazyme Australia, Pty Ltd, Sydney, Australia).

The digestibility

of starch

was calculated as follows: {(starch intake (g) - fecal starch (g)) /starch intake (g)} x 100. Comparison of changes in postprandial blood glucose concentration in mts intubated HAS and CS suspensions (experiment 3)). To evaluate the postprandial blood glucose concentrations of HAS and CS, we used 10 male rats (35 days of age). The animals were acclimatized

for 10

days by the feeding of the standard diet. At age of 45 days, they were divided into groups on the basis of body weight and fasted for 24 h prior to use in oral glucose tolerance test. After 24 h-fast, the control rats were given an 18% CS suspension (w/v) with a stomach tube to provide 225 mg of starch per 100 g body weight. suspension (w/v) in the same manner. time-intervals

indicated in the results.

commercially

available

kit (Glucose

Rats of the test group were given an 18% HAS

Blood samples were collected from the tail vein at Blood glucose concentrations

were determined with a

B-test Wako, Wako Pure Chemical Industries,

Tokyo,

Japan). Statistical analyses. determined

by &i-square

starch digestibility

The statistical

differences

in tumor incidence

analysis with Yates correction

and blood glucose concentration

(19).

between

groups was

The statistical differences

in

between CS and HAS were analyzed by

Student’s t-test. The significance of relationships betweendata was established by linear regression analysis (20).

other statistical

differences were determined

by ANOVA

and then Duncan’s

multiple range test (21). A probability value of c 0.05 was taken to be statistically significant.

STARCH AND MAMMARY TUMOR

1041

RESULTS Tumor induction study (experiment 1).

The final body weights in rats fed the CS, HAS and

WB diets were 313 2 5, 294 f 5 and 319 + 6 g, respectively. the HAS diet was significantly

The final body weight in rats fed

lower than those of rats fed the two other test diets.

Food

intakes in rats fed the CS, HAS and WB diets for 112 days were 1.38 = 0.01, 1.34 + 0.01 and 1.45 2 0.01 kg/rat, respectively.

There were no significant

differences in food intake between

the HAS and CS diet-fed groups. However, food intake in rats fed the WB diet was significantly higher than that in rats fed the HAS diet. Although there were no significant the experiment,

differences in mammary tumor incidence at the end of

the HAS diet retarded the first appearance

(appeared 48 days after DMBA administration) after DMBA administration)

of palpable tumors by 21 days

compared with the CS diet- (appeared 27 days

and the WB diet-fed groups (appeared 30 days after DMBA

administration).

6 5

+ *

3O%HAS 13.6% WB

4 3 2 1

u

0

0

20

40

60

80

100

120

Days after DMBA administration FIG. 1. Cumulative number of palpable tumors per tumor-bearing respective

rat fed the

test diets over 112 days after 7, 12-dimethylbenz[a]anthracene

administration.

Diet abbreviations

used: CS, corn starch diet;

30% high amylose maize starch diet; The statistical differences

30% HAS,

13.6% WB, 13.6% wheat bran diet.

in cumulative

rat between groups at the day examined

palpable tumors per tumor bearing palpable mammary

tumors were

determined by ANOVA and then Duncan’s multiple range test (21). Values not sharing a common superscript letter are significantly

different (p c 0.05).

S. KASAOKA

1042 Figure 1 shows the cumulative

et al.

number of palpable tumors per tumor-bearing

rat fed the

respective test diets over 112 days after DMBA administration.

On day 5.5 and 62 after DMBA

administration,

rat were significantly

cumulative

palpable tumors per tumor-bearing

the HAS and WB diet-fed groups than those in the CS diet-fed group. palpable tumors in the HAS diet-fed group were also significantly diet-fed group on day 90 and 98 after DMBA administration,

lower in

While cumulative

lower than those in the CS

those in the WB diet-fed group

were comparable to those in the CS diet-fed group. The mean tumor numbers per tumor-bearing rat in the CS, HAS and WB diet-fed groups were 6.23 = 0.69, 4.91 = 0.74 and 5.69 c 0.74 at the end of experimental

period, respectively.

The mean tumor weights per tumor-bearing

rat in the

CS, HAS and WB diet groups were 6.90 2 0.93, 5.14 + 0.83 and 4.79 + 0.82 g, respectively. Both mean tumor number and weight per tumor bearing rat reduced by 10~30% in rats fed the HAS and WB diets compared with those in the control diet, but these differences

were not

significant. The results

of fecal dry weight and fecal excretion

of neutral

sterols,

bile acids and

estradiol-17 p were shown in Table 3. Fecal dry weights in rats fed the HAS and WB diets were significantly

higher than that in rats fed the CS diet. In addition, fecal dry weight in rats

fed the WB diet was significantly

higher than that in rats fed the HAS diet. A similar pattern

was seen in fecal excretion of total bile acids with the order of WB > HAS > CS diet-fed groups.

However, in contrast to fecal excretion of total bile acids, fecal excretions of neutral

sterols in rats fed the HAS and WB diets were significantly

lower than that in rats fed the CS

diet. Fecal excretion of estradiol-17 P (free form) in rats fed the HAS diet was almost comparable to that in rats fed the CS diet. But fecal excretion of estradiol-17 S in rats fed the WB diet was about 2.6 fold higher than that in rats fed the CS diet (p c 0.05). TABLE 3 Fecal Dry Weight and Fecal Excretion of Bile Acids, Neutral Sterols and Estradiol-17

@ in Rats Fed the Respective Test Diets *

Fecal dry Diet #

weight

Fecal excretion Neutral sterols ,umol/day

Total bile acids

Estradiol-17 p pmollday

@&day

CS

mg/day 348 2 7 a

5.97 c 0.20 b

10.5 20.3 a

148+43

30% HAS

569 + 28 b

5.25 kO.24 a

16.5 20.7

1012 14 a

b

a

39.6 2 0.7 ’ 382248 b 5.25 20.18 a 1266 223 ’ 13.6% WB * Data are expressed as mean + SE and values not sharing a common superscript letter are significantly different (P -ZO-05), when analyzed by ANOVA and then Duncan’s multiple range test (21). Feces were collected for 3 days (day 27-29 after 7, 12dimethylbenz[a]anthracene administration). # Diet abbreviations used: CS, corn starch diet; 30% HAS, 30% high amylose corn starch diet, 13.6% WB, 13.6% wheat bran diet.

STARCH AND MAMMARY TUMOR Table 4 shows the serum concentration rats fed the respective

diets.

1043

of estradiol-17 p and ovarian aromatase activity in

Serum concentration

of estradiol-17 B was almost the same

among the groups tested. Ovarian aromatase activity in rats fed the HAS diet did not significantly differ from that in rats fed the CS diet. But ovarian aromatase activity in rats fed the WB diet was significantly

higher than that in the rats fed the CS diet. There was a positive correlation

between the ovarian aromatase activity and fecal excretion of estradiol-17 S (Y=119OX+193, R=0.244, P=O.O359), where Y is fecal excretion of estradiol-17 B (pmol/day), and X is specific activity of ovarian aromatase (pm01

min-r

mg protein”).

??

??

TABLE 4 Serum Concentration

of Estradiol-17 p and Ovarian Aromatase

Activity in Rats Fed the Respective Test Diets * Diet #

Estradiol-17 B

Aromatase activity pm01 rnin-r

pmol/L CS

??

355 c 34

mg protein-*

??

0.054 2 0.012 a

30% HAS

343 + 35

0.074 + 0.009

13.6% WB

336 + 23

0.101 $0.016

ab

b

(n=26) (n=23) (n=25)

* Data are expressed as mean = SE and values not sharing a common superscript letter are significantly

different (P < O.OS),when analyzed by ANOVA and then

Duncan’s multiple range test (21).

Serum and ovaries were collected on day

112 after 7, 12. dimethylbenz[a]anthracene # Diet abbreviations

administration.

used: CS, corn starch diet; 30% HAS, 30% high amylose corn

starch diet; 13.6% WB, 13.6% wheat bran diet.

Compankon of aYge&ili@ of IUS and CS in ileorectostomized rats (experiment 2). digestibilities

in ileorectostomized

Starch

rats fed the 65.5% HAS and 65.5% CS diets were 66.5 c

0.5% and 99.6 2 0.05%, respectively, and this difference was significant (P < 0.0001).

Comparison of changes in postpmndial blood glucose concentration in mts intubated HAS and CS suspensions (experiment 3). administered

with HAS and CS suspensions.

Figure 2 shows blood glucose responses

in rats

The rises in blood glucose concentration

significantly depressed at 30,45 and 60 min after gastric intubation of the HAS suspension.

were

S. KASAOKA et al.

1044

0’

B

0

’ 30

’

’ 60

n

’ 90

-D-

225 mg corn starch

d

225 mg HAS

n

’ 120

s

’ ’ 1 150 180

Time (min) FIG. 2. Comparison of changes in postprandial blood glucose concentration in rats intubated

225 mg high amylose corn starch or 225 mg corn starch

* Denotes a significant difference between high amylose corn

suspensions.

starch and corn starch suspensions at that time point (P < 0.05). The statistical differences were determined by Student’s t-test. DISCUSSION Increasing the amount of RS in a diet or food may reduce the energy density, that has been suggested for dietary fiber.

In this regard, successive intake of RS for a long term may be of

benefit in preventing the obesity-related

diseases such as an insulin independent

diabetes and

breast cancer. The present study showed that the cumulative numbers of palpable tumors per tumor-bearing rat were significantly

lower in rats fed the HAS and WB diets than in rats fed the CS diet in the

middle of experimental

period.

First appearance of palpable tumor was also retarded in rats

fed the HAS and WB diets than in rats fed the CS diet. in the small intestine was approximately digested.

hr general, DMBA-induced

rats was also significantly

depressed

CS.

mammary tumor is thought to be closely associated with calorie

intake and serum estrogen level (12). concentration

66% in contrast to CS which was almost completely

Blood glucose response in HAS-intubated

compared with that in rats administered

We found that the digestibility of HAS

However, in our results neither serum estradiol-17 p

nor fecal excretion of estradiol-17 l3 was not affected in rats fed the HAS diet.

Serum estradiol-17 R concentration

in rats fed the WB diet was also comparable to that in rats

fed the CS diet, although the fecal excretion of estradiol-17 P in rats fed the WB diet was

STARCH AND MAMMARY TUMOR

almost 3 times higher than that in rats fed the CS diet. previous report of Cohen et al. (ll),

1045

These results were comparable to the

in which they reported a WB-supplemented

diet did not

decrease serum concentration

of estradiol-17 I3 , regardless of exerting an inhibitory effect on

mammary tumor progression.

They suggested that the effect of WB was probably ascribed to

fecal energy loss, possibly due to the reduced fat absorption.

In our study, fecal excretion of

total bile acids in rats fed the WI3 diet was 3.5 times higher than that in rats fed the CS diet. This may reinforce the interpretation against mammary

of Cohen et al. (11) for the inhibitory mechanism

tumor progression.

Taking into account the facts mentioned

suggest that HAS and WI3 have the same mechanism tumor progression,

in which physiological

for the inhibitory

of WB

above, we

effects on mammary

loss in energy due to low digestibility

of HAS is

responsible rather than changes in serum estradiol-17 p concentration. Another possible mechanism response of insulin.

of inhibitory

effect of HAS on tumor progression

is a low

Imagawa et al. (22) reported that insulin was shown to be a growth factor

for normal and malignant breast cells in vitro. be a growth factor for DMBA-induced energy restriction had significantly

Klurfeld et al. (4) suggested that insulin might

tumor, because the groups subjected

to 30 and 40%

reduced serum levels of insulin in the fasting state, with

delaying first appearance of tumor in rats subjected to 30% and 40% energy restriction compared with the group fed ad libitum.

In our study we did not measure blood insulin concentration,

but we found that postprandial

serum glucose of rats administered with HAS was significantly

lower than that of rats administered with CS. There are many reports that HAS produces lower areas under the glucose

and insulin

response

curves than CS does (23-25).

In separate

experiments, we found that ratios of lipid to protein contents in carcass of rats fed 40% HAS diets was significantly

lower than those of rats fed CS (data not shown).

This also suggests

that serum insulin level is lower in rats fed the HAS diet than that in rats fed the CS diet. Finally, we suggest that HAS exerts inhibitory

effects on progression of DMBA-induced

mammary tumor through the mild caloric restriction Therefore, chronic consumption

and favorably

low response of insulin.

of HAS might be beneficial in preventing mammary tumor in

the same manner as dietary fiber. ACKNOWLEDGEMENTS We gratefully thank Hiroyuki Nishikawa for technical assistance. REFERENCES 1. Rose DP. Dietary factors and breast cancer. Cancer Surv 1986; S(3): 671-87. 2. KIurfeld DM, Weber MM, Kritchevsky D. Inhibition of chemically induced mammary and colon tumor promotion by caloric restriction in rats fed increased dietary fat. Cancer Res 1987; 47: 2759-62. 3. Sylvester PW, Aylsworth CF, Van Vugt DA Meites J. Influence of underfeeding during the “critical period” or thereafter on carcinogen-induced mammary tumors in rats. Cancer Res 1982; 42: 4943-7.

1046

SKASAOKAetal.

4. Klurfeld DM, Welch CB, Davis MJ, Kritchevsky D. Determination of degree of energy restriction necessary to reduce DMBA-induced mammary tumorigenesis in rats during the promotion phase. J Nutr 1989; 119: 286-91. 5. Kritchevsky D, Weber MM, Klurfeld DM. Dietary fat versus caloric content in initiation and promotion of 7,12-dirnethylbenz[a]anthracene-induced mammary tumorigenesis in rats. Cancer Res 1984; 44: 3174-7. 6. Position of theAmerican Dietetic Association: health implications of dietary fiber, J Am Diet Assoc 1993; 93: 1446-7. 7. Truswell AS. Evolution of dietary recommendations, goals, and guidelines, Am J Clin Nutr 1987; 45: 1060-72. 8. Diet, nutrition, and prevention of chronic diseases. 797:109-15.

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