Influence of Kiwi Fruit on Immunity and Its Anti-oxidant ...

Food Sci. Technol. Res., 16 (2), 135–142, 2010

Influence of Kiwi Fruit on Immunity and Its Anti-oxidant Effects in Mice

Haruyo iwaSawa1*, Erika Morita

1, Hiroshi ueda2 and Masatoshi yaMazaki

1

1 Department of Medical Life Chemistry, Faculty of Pharmaceutical Sciences, Teikyo University, 1091-1 Sagamiko-machi, Sagamihara

City, Kanagawa 229-0195, Japan2 National Institute of Vegetable and Tea Science, National Agriculture and Food Research Organization, 360 Kusawa, Ano, Tsu, Mie

514-2392, Japan

Received July 1, 2009; Accepted November 20, 2009

We have been investigating the immunopotentiating activity (biological response modifier (BRM)-like activity) of different fruits and attempting to clarify whether the level of this activity is consistent with the content of vitamins or other major nutrients in these fruit. In this study, we focused on kiwi fruit, which contains vitamin C and polyphenol and has a high BRM-like activity and anti-oxidant activ-ity. We evaluated differences in this activity according to the strain and maturity. To determine the anti-oxidant effects of oral kiwi fruit intraperitoneal administration, mice were administered kiwi fruit juice. It was found that the BRM-like activity of green kiwi fruit was slightly higher than that of gold kiwi fruit, but the differences were slight between strains and maturity level. After oral administration of kiwi fruit juice to mice, cytokine production increased. The evaluation of urinary oxidative stress markers revealed marked inhibition of in vivo oxidative stress following oral kiwi fruit administration. These results suggest that kiwi fruit intake has beneficial effects on the body, increasing cytokine production and exerting anti-oxidant effects.

Keywords: kiwi fruit, biological response modifier-like activity, anti-oxidant effect, 8-hydroxy-2’-deoxyguanosine,

N-epsilon-(hexanoyl)-lysine

*To whom correspondence should be addressed.

E-mail: [email protected]

IntroductionPeople concerned with achieving a healthy diet have

mainly focused on nutritional balance. However, consider-

ing that food intake also has effects other than nutrition, we

have been investigating the effects of food on immunity

(Yamazaki and Ueda, 1997b; Yamazaki and Ueda, 2000).

Nutrient intake is necessary to maintain an effective immune

system, although food contains not only nutrients but also

large amounts of non-nutrients (phytochemicals). Therefore,

phytochemicals are also considered to markedly affect the

body. Indeed, phytochemicals have been shown to play an

important role in defending the body from diseases. We have

clarified the anti-inflammatory, anti-allergic, and anti-cancer

effects of phytochemicals (Yamazaki and Ueda, 1997a; Ueda

and Yamazaki, 1997; Ueda and Yamazaki, 2003; Ueda et al.,

2002). We have also evaluated the immunopotentiating activ-

ity of familiar vegetables and fruits such as the neutrophil-

increasing activity and priming activity for the induction of

tumor necrosis factor (TNF)-α (Yamazaki and Ueda, 1997b;

Iwasawa and Yamazaki, 2009).

Phagocytes represented by macrophages migrate to,

and accumulate in, places where foreign materials are pres-

ent. Upon stimulation or activation, phagocytes produce

cytokines such as interleukin (IL)-1, IL-6, IL-12, TNF-α,

and interferon (Yamazaki and Iwasawa, 2004). Therefore,

materials that can induce phagocytes or increase cytokine

production have immunopotentiating effects. Two-step stim-

ulation (priming and triggering stimulation) is necessary for

macrophages to produce cytokines such as TNF-α. Priming

stimulation is indispensable for macrophage activation, and

the immunopotentiating activity of food components can be

assessed by evaluating the priming activity for cytokine in-

duction. Kiwi fruit, bananas, and apples have shown marked

immunopotentiating effects (Yamazaki and Ueda, 2000; Iwa-

sawa and Yamazaki, 2009). Most previous studies on kiwi

fruit have dealt with their allergy-causing effects (Lucas et

al., 2005; Chen et al., 2006; Bublin et al., 2004). There have

been few studies on its immunopotentiating activity and

no studies have compared this activity between kiwi fruit

strains or maturity level. Therefore, we evaluated the in vitro

and in vivo immunopotentiating activity of kiwi fruits using

neutrophil-accumulating activity, morphological changes in

macrophages, and priming activity for cytokine induction as

parameters. In addition, differences in activity according to

the kiwi fruit strain and maturity were also evaluated using

green and gold kiwi fruits.

We focused on phytochemicals containing polyphenols

which have anti-oxidant activity. Our previous study found

a higher polyphenol content in kiwi fruit than in other fruits

(Yamazaki et al., 2000). The body is exposed to various oxi-

dative stresses. Active oxygen species and free radicals react

with biomolecules and tissues, causing carcinogenesis and

arteriosclerosis (Halliwell and Gutteridge, 2007). Therefore,

in vivo inhibition of excessive oxides is important for pre-

venting diseases.

Recently, the anti-oxidant activities of polyphenols con-

tained in various foods, mainly tea and fruits, have been

reported (Tanaka and Suzuki, 2004; Yoshino et al., 2006;

Scalzo et al., 2005). There have been studies on the in vitro

anti-oxidant activity of kiwi fruit (Collins et al., 2001; Jung

et al., 2005), but few studies on its in vivo anti-oxidant activ-

ity. Therefore, we evaluated the in vivo anti-oxidant effects of

kiwi fruit on immunity using two markers. One marker was

8-hydroxy-2’-deoxyguanosine (8-OHdG), the most common

marker currently used. The urinary 8-OHdG level reportedly

increases with risk factors such as diabetes mellitus, athero-

sclerosis, and smoking (Wu et al., 2004; Pilger and Rudiger,

2006). The second marker was N-epsilon-(hexanoyl)-lysine

(HEL), which has attracted attention as a marker of early

stage lipid peroxidation. HEL is associated with rheumatoid

arthritis and arteriosclerosis (Fukuchi et al., 2008; Kageyama

et al., 2008). Some recent studies have shown that the intake

of foods containing anti-oxidants reduces 8-OHdG (Thomp-

son et al., 1999; Dhawan and Jain, 2005), but there have

been only a few studies on the 8-OHdG level after kiwi fruit

intake (Collins and Harrington, 2003) and no study on HEL.

Therefore, we evaluated changes in these two markers of

oxidative injury after oral (p.o.) kiwi fruit administration to

mice.

Materials and MethodsKiwi fruit For this study, we selected Hayward (Actin-

idia deliciosa), the most common commercially available

breed of kiwi, Zespri green kiwi, and Hort16A (Actinidia

chinensis), which is known as Zespri gold kiwi. These kiwi

fruits were donated by Zespri Co., Ltd. We established four

points of maturity on the basis of a hardness meter: 2.0, 1.5,

1.0 and 0.5, where 2.0 is hard and 1.0-0.5 are considered in

season. The flesh was weighed, cut into appropriate sizes,

and mixed using a mixer for 30 s. Each homogenate was

centrifuged (High-capacity refrigerated centrifuge 8800,

Kubota Co., Ltd., Tokyo, Japan) at 3000 rpm for 10 min, and

the resulting supernatant was passed through a filter. Each

supernatant was centrifuged at 16,000 rpm for 1h (Automatic

high speed refrigerated centrifuge 20PR-52, Hitachi Koki

Co., Ltd., Tokyo, Japan), and the suspended substances were

removed to obtain the sample solution. The osmotic pressure

and pH of the sample were adjusted for intraperitoneal (i.p.)

administration.

Mice Male ICR mice (5 or 6 weeks old) were purchased

from Sankyo Labo Service Corp., Inc. (Tokyo, Japan). C3H/

HeNCrl mice (6 weeks old) were purchased from Oriental

Yeast Co., Ltd. (Tokyo, Japan). The animals were given a

standard laboratory diet and water ad libitum. Experiments

were conducted following the Guidelines for Animal Experi-

mentation (No. 105) and Notification (No. 6) implemented

by Ministry of Education, Culture, Sports, Science and Tech-

nology, Japan.

Media RPMI1640 was purchased from Sigma Aldrich

Co. (St. Louis, MO, USA) and used for the incubation of

peritoneal cells.

Measurement of accumulated neutrophils Male ICR

mice were injected i.p. with 0.5, 0.25 or 0.05 mL of kiwi fruit

juice. Peritoneal exudate cells (PEC) were collected in 5 mL

saline after 6 h and added to 200 μL FCS. Some of the PEC

were stained with Türk reagent (Wako Pure Chemical Indus-

tries, Osaka, Japan) and counted under a light microscope.

A portion of the remaining cells was placed on a glass slide,

using an auto cell smear, to assess the percent of neutrophils

in PEC by direct counting under a light microscope.

In vitro observation of differences in macrophage mor-

phological changes PEC were collected in saline from

male C3H/HeNCrl mice, and cultured in 24-well plates at 3.0

× 104 cells/mL of 5% fetal calf serum (FCS) in RPMI me-

dium per well at 37℃ under 5% CO2 for 2 h. The wells were

washed twice with warm phosphate-buffered saline (PBS)

(-) before the addition of 1 mL of 5% FCS-RPMI containing

kiwi fruit juice (10%). The wells were observed under a light

microscope from days 1 to 7.

Measurement of priming activity for cytokine production

after i.p. administration Male ICR mice were injected i.p.

with 0.25 mL of kiwi fruit juice. PEC were obtained after

4 days. These cells were cultured in 96-well plates at 1.0 ×

106 cells in 200 μL of 5% FCS-RPMI/well at 37℃ under

5% CO2 for 2 h. Supernatant (100 μL) was discarded and

replaced with 100 μL of 5% FCS-RPMI containing 10 μg

of Enterococcus faecalis for triggering stimulation. After 2

h. iwaSawa et al.136

h, the TNF-α concentration of the culture supernatant was

evaluated by ELISA (Endogen, Pierce Biotechnology, Inc.,

Rockford, IL, USA). After 24 h, the IL-12 concentration of

the culture supernatant was evaluated by ELISA.

Measurement of priming activity production after p.o.

administration Male ICR mice were p.o. administered 1%

or 5% kiwi juice (hardness was about 1.0) for 8 days ad libi-

tum. The control group was p.o. administered distilled water.

PEC were obtained and cultured in 96-well plates at 1.0 ×

106 cells in 200 μL of 5% FCS-RPMI/well at 37℃ under

5% CO2 for 2 h. Supernatant (100 μL) was discarded and

replaced with 100 μL of 5% FCS-RPMI containing 10 μg of

E. faecalis for triggering stimulation. After 2 h, the TNF-α

concentration of the culture supernatant was evaluated by

ELISA (Endogen). After 24 h, the IL-12 concentration of the

culture supernatant was evaluated by ELISA.

Measurement of urinary oxidative stress markers after

p.o. administration Male ICR mice were p.o. administered

1% or 5% kiwi juice (hardness was about 1.0) for 8 days ad

libitum. The control group was p.o. administered distilled

water. We collected urine for 2 h 3 times: before p.o. admin-

istration, and days 4 and 8 after p.o. administration. Urinary

8-hydroxy-2’-deoxyguanosine (8-OHdG) and N-epsilon-

(hexanoyl)-lysine (HEL) were evaluated by ELISA (Japan

Institute for the Control of Aging, Nikken Seil Co., Ltd., Fu-

kuroi, Japan).

ResultsNeutrophil-accumulating activity of kiwi fruits In gen-

eral, the intraperitoneal leukocyte count of mice is about 5

× 106 cells/mouse. However, the leukocyte count was 7 ×

106 cells/mouse, even in the mice injected i.p. with 0.05 mL

of kiwi fruit juice, and markedly increased to 15-20 (× 106)

cells/mouse in mice injected i.p. with 0.5 mL of juice (Fig.

1A). Neutrophils generally account for about 5% of all intra-

peritoneal cells, but the percentage increased to 40-60% in

the 0.05-mL administration group and 70-80% in the 0.5-mL

administration group (Fig. 1B). Thus, i.p. kiwi fruit admin-

istration dose-dependently increased both the intraperitoneal

leukocyte count and neutrophil percentage. The effects of

green kiwi were more marked than those of gold kiwi, but

the difference was slight. Subsequently, to evaluate possible

differences among maturity levels, four maturity levels from

hard to soft were measured using a hardness tester. At all

maturity levels, there was a constant marked increase in the

total intraperitoneal cell count and neutrophil accumulation

with negligible differences among the maturity levels (Fig.

2A and B). The effects of green kiwi were more marked than

those of gold kiwi. These results showed that kiwi fruit juice

has marked immunopotentiating effects (biological response

modifier (BRM)-like activity), increasing the leukocyte count

and recruiting neutrophils to local areas.

In vitro morphological changes in macrophages Upon

activation by the recognition of foreign materials, macro-

phages as phagocytes migrate to areas where foreign mate-

rials are present, extend their pseudopodia to engulf them.

Since kiwi fruit juice administration increased the leukocyte

count, morphological changes in macrophages were evalu-

ated. Macrophages in the intraperitoneal cavity of normal

mice were collected and cultured in a medium containing


Fig. 1. Dose-dependent neutrophil accumulation following intraperitoneal injection of green or gold kiwi fruit juice.

Male ICR mice were injected i.p. with 0.5 or 0.05 mL of kiwi fruit juice. The data show means ± S.D. (n=3). A: Total cell number of peritoneal exudate cells (PEC). B: Proportion of neutrophils in PEC. Statistical differences were analyzed by Dunnett’s test. A and B: **P<0.01, compared with the control (non-treated) group.

0

10

20

30

40

Control 0.05 0.5

Kiwi juice (mL/mouse)

Tot

al n

umbe

r of

PE

C (

x10

6 cel

ls/m

ouse

)

Green kiwi Gold kiwi

**

**

A

0

20

40

60

80

100

Control 0.05 0.5

Kiwi juice (mL/mouse)

Pro

port

ion

of n

eutr

ophi

ls (

%)

**

**

****

Green kiwi Gold kiwi

B

137

10% kiwi fruit, and their morphology was evaluated using

a microscope for one week (Fig. 3). Even after 1 day of cul-

ture, morphological changes occurred. After 3 days, a few

elongated cells were observed even in the controls cultured

without kiwi fruit, and many elongated macrophages were

present in cells cultured with green or gold kiwi fruit. This

change was the most marked after 2-3 days of culture. After

7 days of culture, most control cells had died, while there

were many surviving cells among those cultured with kiwi

fruit. These results suggest that some constituents in kiwi

fruit juice not only activate macrophages by changing their

shape, but also extend their longevity. Although these effects

were not observed in cells after the addition of 0.5% kiwi

juice, they were confirmed after the addition of 5% juice.

Differences among the maturity levels and between strains

appeared to be slight.

In vivo priming effects of kiwi fruits on cytokine produc-

tion Since neutrophil accumulation and morphological

changes in macrophages after kiwi fruit i.p. administration

were confirmed, BRM-like activity was evaluated using

priming effects as a parameter. The priming effects of kiwi

fruits on TNF-α and IL-12 were confirmed in all samples

(Fig. 4A and B). Differences among the maturity levels were

slight. The effects of green kiwi fruit were more marked than

those of gold kiwi, but the difference was small.

After confirming the priming effects of i.p. kiwi fruit ad-

ministration, the priming effects by p.o. administration were

evaluated using kiwi fruit juice. As differences according to

h. iwaSawa et al.

Fig. 2. Differences in neutrophil accumulation by intraperitoneal injection according to kiwi fruit strain and hardness level.

Male ICR mice were injected i.p. with 0.25 mL of kiwi fruit juice. The data show means ± S.D. (n=3). A: Total cell number of peritoneal exudate cells (PEC). B: Proportion of neutrophil in PEC. The x-axis represents the hardness level of kiwi fruit as a maturity level. Statistical differences were analyzed by Dunnett’s test. A and B: *P<0.05 and **P<0.01, compared with the control (non-treated) group.

0

5

10

15

20

2.5 2.0 1.5 0.5

Hardness

Tota

l num

ber

of

PEC

(×

106

cells

/m

ouse

)

Control Green kiwi Gold kiwi

**

*

****

*

A

0

20

40

60

80

100

2.5 2.0 1.5 0.5

Hardness

Pro

port

ion o

f neutr

oph

ils (

%)


**

**

**

**

**

**

**

**

B

A B C

Fig. 3. In vitro morphological changes in macrophages according to the type of kiwi fruit. The cells were observed under a light microscope for 1 week. Photos were taken after 3 days and the hardness of kiwi fruits was 0.5. A: Saline. B: Green kiwi. C: Gold kiwi.

138

maturity level were considered slight based on previous ex-

periments, kiwi fruit with a mean hardness of 1.0, indicating

they are ready to eat, were used. TNF-α was not induced in

the absence of triggering in the kiwi fruit-intake groups, the

same as in the water-intake control group. After triggering,

the concentration of induced TNF-α was lower in the 1%

gold and 5% green kiwi fruit-intake groups than in the con-

trol group (Fig. 5A). Without triggering, the concentration of

induced IL-12 was lower in the green kiwi fruit-, but higher

in the gold kiwi fruit-intake groups than in the control group

(Fig. 5B). After triggering, no change was observed in the

1% gold kiwi fruit-intake group, but the concentration of in-

duced IL-12 was lower in the other kiwi fruit-intake groups

than in the water intake group. With 5% kiwi fruit juice,

similar data were obtained in 3 independent experiments. Al-

though there were no statistical differences, cytokine produc-

tion slightly increased after p.o. administration of 10% kiwi

fruit juice (date not shown).

Reduction in urinary oxidative stress markers by p.o. kiwi

fruit administration The concentration of 8-OHdG as a

marker of DNA oxidative injury increased until day 4 in the

water-intake control group, but was maintained at the level

before p.o. administration (day 0) in the kiwi fruit-intake

group (Fig. 6). On day 8 of p.o. administration, the 8-OHdG

concentrations in the green kiwi fruit-intake groups in-

creased, but were lower than those in the control group, and

those in the gold kiwi fruit-intake groups were maintained

at low levels. The difference in the 8-OHdG concentration

between the two green kiwi fruit concentrations was small,

while the 8-OHdG concentration in the 1% gold kiwi fruit-

intake group was lower than that in the 5% gold kiwi fruit-

intake group.

The concentration of HEL reflecting the early stage of

lipid peroxidation was lower in the 1% green kiwi fruit-

intake group than in the control group on day 4 and in the

5% green kiwi fruit-intake group than in the control group on

day 8 (Fig. 7). The HEL concentrations in the gold kiwi fruit-

intake groups were markedly lower than that in the control

group on day 4, and these values were maintained on day 8.

As for gold kiwi fruit, the HEL concentration, as well as the

8-OHdG concentration was lower in the 1% than 5% kiwi

fruit-intake group. In terms of both 8-OHdG and HEL, gold

kiwi fruit exhibited more marked anti-oxidant effects than

green kiwi fruit.

DiscussionWe evaluated the BRM-like activity of kiwi fruits quan-

titatively and qualitatively to determine whether this activ-

ity differs according to strain or maturity. We found that the

BRM-like activity of kiwi fruit increased dose-dependently,

but negligibly with maturity level. Between the strains, green

kiwi showed more marked activity than gold kiwi, but the

difference was slight. Kiwi fruit induced morphological

changes in macrophages, but these changes did not differ

according to the strain or maturity. In contrast, our previous

study on bananas found variations in BRM-like activity ac-

cording to the strain and maturity (Iwasawa and Yamazaki,

2009). These results suggest that maturity-associated chang-

es in BRM-like activity differ among the different kinds of

fruit.


Fig. 4. Differences in the priming activity of intraperitoneal injection on cytokine production according to kiwi fruit strain and hardness level.

The data show means ± S.D. (n=3). A: Tumor necrosis factor (TNF)-α concentration in the culture supernatant. B: Interleukin (IL)-12 con-centration in the culture supernatant. The x-axis represents the hardness level of kiwi fruit as the level of maturity. Statistical differences were analyzed by Dunnett’s test. A and B: *P<0.05, **P<0.01, compared with the control (non-treated) group.

0

200

400

600

800

1000

1200

2.0 1.5 1.0 0.5

Hardness

TN

F- a

(pg

/mL)


***

*

*

A

0

3000

6000

9000

12000

1.0 0.51.52.0

Hardness

IL-1

2 (p

g/m

L)

**

*

**

**

**

15000

B

139

The priming activity for cytokine induction was con-

firmed by i.p. administration. After p.o. administration, cyto-

kine induction due to triggering decreased. However, without

triggering, the concentration of induced IL-12 was higher in

the gold kiwi fruit-intake group than in the control group. Al-

though there was no statistical differences, cytokine produc-

tion slightly increased after p.o. administration of 10% kiwi

fruit juice. These results suggest that kiwi fruit intake en-

hances cell-mediated immune function and this effect varies

according to the concentration of kiwi fruit. In recent years,

studies on the prevention of diseases by food components

have been extensively performed (Tanaka and Suzuki, 2004;

Yu and Paetan, 2006). The effects of compounds contained in

daily meals may not be as marked as those of clinical drugs.

However, efforts to eat foods exhibiting BRM-like activity

may increase immunocapacity to some degree. Knowledge

of functional foods in the planning of meals could contribute

to individuals' improvement in immunocapacity and preven-

tion of various diseases.

Since kiwi fruit contains vitamin C and polyphenol,

which has anti-oxidant activity, the in vivo anti-oxidant ef-

fects of p.o. kiwi fruit administration were also evaluated in

mice. We found that markers of oxidative stress, (8-OHdG

and HEL, decreased after kiwi fruit juice intake. Both green

and gold kiwi fruits were confirmed to show this activity, but

the latter exhibited more marked effects. We also compared

the in vitro anti-oxidant activity between green and gold kiwi

fruits, and observed more marked activity in the latter (in

preparation). This study confirmed not only the in vitro, but

also the in vivo anti-oxidant activity after p.o. administration,

and also suggested that the latter activity differs according

to the strain. However, the activity may not depend on the

h. iwaSawa et al.

Fig. 5. Differences in the priming activity of p.o. administration on cytokine production according to kiwi fruit strain and hardness level.

The data show means ± S.D. (n=8). A: Tumor necrosis factor (TNF)-α concentration in the culture supernatant. B: Interleukin (IL)-12 con-centration in the culture supernatant. The x-axis represents the hardness level of kiwi fruit as the level of maturity. Statistical differences were analyzed by Dunnett’s test. A and B: *P<0.05 and **P<0.01, compared with the distilled water group.

0

50

100

150

200

250

300

350

400

Distilled water Green kiwi 1% Green kiwi 5%Gold kiwi 1% Gold kiwi 5%

TN

F-

(pg/

mL)

Enterococcus faecalis(+) Enterococcus faecalis(-)

**

0

50

100

150

200

250

300

350

Distilled water Green kiwi 1% Gold kiwi 1% Green kiwi 5% Gold kiwi 5%

IL-1

2(p

g/m

L)

Enterococcus faecalis(+) Enterococcus faecalis(-)

**

**

**

*

B

A

140

concentration gradient because our results found a higher ac-

tivity of 5% than 1% juice for green kiwi fruit, and 1% than

5% juice for gold kiwi fruit. Anti-oxidants such as vitamin

C have been reported to not only show anti-oxidant activity,

but also act as oxidants (Chen et al., 2008). There may be an

appropriate intake amount for each food, and a higher intake

may not always result in more marked effects. We specu-

late that green kiwi with a low anti-oxidant activity shows

marked effects at a concentration of 5%, while gold kiwi

with a high anti-oxidant activity reduces oxidative stress

markers more markedly at a concentration of 1%, i.e., at 5%

gold kiwi fruit shows an extremely high activity.

The negligible influence of the maturity of kiwi fruits

on BRM-like activity observed in this study suggests that

the concentration of the active component is similar among

maturity levels. Since the strain showing higher BRM-like

activity differed from that showing higher anti-oxidant activ-

ity, the component causing the former may differ from that

causing the latter. The separation and identification of these

components will be necessary in the future. Although the

link between anti-oxidant activity and immunopotentiation

could not be confirmed, kiwi fruit intake is expected to pro-

duce anti-oxidant effects, and help prevent diseases such as

atherosclerosis and carcinogenesis. As the protease actinidin


0

50

100

150

200

250

300

350

400

Time

Con

cent

r at i o

nof

8-O

HdG

( ng /

mL)

Distilled water Green kiwi(1%)

Green kiwi(5%)

Gold kiwi(1%)

Gold kiwi(5%)

* *

*

*

*

day0 day4 day8

0

500

1000

1500

2000

Time

Co n

cent

r ati o

nof

HE

L (n m

o l/ L

)

*

**

**

**

**

**

day0 day4 day8

Distilled water Green kiwi(1%)

Green kiwi(5%)

Gold kiwi(1%)

Gold kiwi(5%)

Fig. 7. Variation in urinary N-epsilon-(hexanoyl)-lysine (HEL) levels after p.o. administration of kiwi fruit.

The data show means ± S.D. (n=8). The x-axis represents the time after p.o. administration of kiwi fruit. “Day 0” is before p.o. administra-tion of kiwi fruit. “Day 4” and “Day 8” are days 4 and 8 after p.o. administration of kiwi fruit, respectively. Statistical differences were ana-lyzed by Dunnett’s test. A and B: *P<0.05 and **P<0.01, compared with the distilled water group.

Fig. 6. Variation in urinary 8-hydroxy-2’-deoxyguanosine (8-OHdG) levels after p.o. administration of kiwi fruit.

The data show means ± S.D. (n=8). The x-axis represents the time after p.o. administration of kiwi fruit. “Day 0” is before p.o. administra-tion of kiwi fruit. “Day 4” and “Day 8” are days 4 and 8 after p.o. administration of kiwi fruit, respectively. Statistical differences were ana-lyzed by Dunnett’s test. A and B: *P<0.05 and **P<0.01, compared with the distilled water group.

141

is a well-known functional constituent in kiwi fruit, further

studies will attempt to clarify whether actinidin is a candi-

date for BRM-like substance. At present, a study on the anti-

oxidant effects of kiwi fruit intake in healthy volunteers is in

progress.

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