The Effects of Yellow Soybean, Black Soybean ... - Hogrefe eContent

Int. J. Vitam. Nutr. Res., 80 (2), 2010, 97 – 106

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Original Communication

The Effects of Yellow Soybean, Black Soybean, and Sword Bean on Lipid Levels and Oxidative Stress in Ovariectomized Rats Jae Soon Byun, Young Sun Han and Sang Sun Lee Department of Food & Nutrition, Hanyang University, Seoul, South Korea Received for publication: May 11, 2009; Accepted for publication: January 19, 2010

Abstract: Soy isoflavones have been reported to decrease the risk of atherosclerosis in postmenopausal women. However, the effects of dietary consumption of soybean have not been explored. In this study, we evaluated the effects of consuming yellow soybeans, black soybeans (Glycine max), or sword beans (Canavalia gladiate) on lipid and oxidative stress levels in an ovariectomized rat model. Forty-seven nine-week-old female rats were ovariectomized, randomly divided into four groups, and fed one of the following diets for 10 weeks: a diet supplemented with casein (NC, n = 12), a diet supplemented with yellow soybean (YS, n = 12), a diet supplemented with black soybean (BS, n = 12), or a diet supplemented with sword bean (SB, n = 11). Plasma triglyceride (TG) levels in the BS and SB groups were significantly lower than that in the NC group. Notably, the BS group had significantly lower plasma total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) levels than the other groups. Hepatic total lipid levels were significantly lower in the YS and SB groups, and cholesterol levels were significantly lower in the SB group than in the NC group. Superoxide dismutase (SOD) and catalase (CAT) activities were significantly higher in the groups fed beans compared to the NC group. Hepatic thiobarbituric acid reactive substances (TBARS) levels were also significantly lower in the BS and SB groups than the NC group. In conclusion, our results suggest that consumption of various types of beans may inhibit oxidative stress in postmenopausal women by increasing antioxidant activity and improving lipid profiles. Notably, intake of black soybean resulted in the greatest improvement in risk factors associated with cardiovascular disease. Key words: Yellow soybean, black soybean, sword bean, lipid metabolism, antioxidant enzyme activities.

DOI 10.1024/0300–9831/a000010

Int. J. Vitam. Nutr. Res., 80 (2), 2010, © Hogrefe & Huber Publishers

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J.S. Byun et al.: Effect of Various Beans on Lipid Metabolism

Introduction Hypercholesterolemia is regarded as a major risk factor for the development of atherosclerosis and coronary heart disease (CHD) [1]. Atherosclerotic cardiovascular disease is the primary cause of mortality in many societies throughout the world [2]. Free radical-induced lipid peroxidation is associated with the pathogenesis of atherosclerosis, and reactive oxygen molecules are known to be initiators of lipid peroxidation [3]. Endogenous antioxidant enzymes, such as superoxide dismutase (SOD) and catalase (CAT), as well as antioxidant nutrients, can help to protect cells against free radical damage. Antioxidant enzymes therefore play an important role in controlling lipid peroxidation [4]. Among premenopausal women, CHD is rare, and the overall incidence of cardiovascular complications are much lower than in men of similar age, but the incidence of CHD increases considerably after menopause [5, 6]. Menopause is associated with ovarian hormone deficiency, which results in many physiological changes, including increased levels of low-density lipoprotein (LDL) and total cholesterol, leading to an increased risk of atherosclerotic cardiovascular disease [7, 8]. Soy protein has gained considerable attention because of its potential to improve risk factors for cardiovascular disease. The US Food and Drug Administration (FDA) approved labeling of food containing soy protein as protective against CHD [9]. Whole soybeans contain large amounts of isoflavones, anthocyanins, and other phytochemicals that have beneficial effects on the prevention of menopause symptoms in humans and in an ovariectomized rat model [10, 11]. Epidemiological studies have suggested that consumption of soybeans has protective effects against cardiovascular disease as demonstrated by the low plasma cholesterol levels of East Asian populations [12]. While the cholesterol-lowering properties of soybean are widely accepted, the cholesterol-lowering mechanism is not yet fully understood. Nevertheless, it is presumed to be a result of the isoflavones present in soybean, as well as other components [13, 14]. Isoflavones found in soybeans include daidzein and genistein, and these are good candidates for the cardio-protective effects of soybean because of their biological and chemical similarities to estrogens [15]. Furthermore, anthocyanins are able to react with many active substances in the human body because of their structure, particularly the presence of hydroxyl groups [16]. Anthocyanins, as one of the most abundant and widely distributed flavonoids in plants, give most fruits an attractive color and also contribute greatly to the

antioxidant properties of certain colorful foods [17, 18]. In Korea, soybeans and their processed products are commonly eaten to supplement the low protein content of rice. Koreans usually ingest at least one or more types of soybean or soybean-products with every meal [19]. Black soybeans (Glycine max (L.) Merr.) are used as medicinal materials in Asia, and contain natural antioxidants, including anthocyanins, in their seed coats [20,21]. Anthocyanins can scavenge free radicals and inhibit lipid peroxidation and DNA damage. They may also decrease the risk of coronary heart disease and atherosclerosis by inhibiting the oxidation of lowdensity lipoprotein (LDL) [22, 23]. Sword beans (Canavalia gladiate) belong to the Leguminosae (Fabaceae) family, Phaseloeae tribe, Diocleinae subtribe, and originated either in Africa or southern Asia [24]. Sword beans are excellent sources of starch (35 – 45 %) and protein (22 – 29 %), with a good balance of amino acids [25]. Sword beans have numerous traits that are currently exploited, and have the potential to be valuable in both the phytopharmaceutical and nutraceutical industries [26]. Despite their desirable traits, however, there has been little agronomic development of sword beans, hence sword bean seeds are not universally utilized as a food source. We hypothesized that the different phytochemicals compositions of different beans would have different effects on the lipid profiles, lipid peroxidation levels, and antioxidant enzyme activities of ovariectomized rats. To address this hypothesis, we used whole beans rather than extracts in our experiments. Furthermore, we focused on investigating beans that Koreans commonly consume.

Materials and Methods Animals and diets Forty-seven eight-week-old female Sprague-Dawley (SD) rats weighing between 163 and 164 g were purchased from Daehan Biolink Co. Ltd. (Chungcheongbuk-do, Korea). The animals were all individually housed in stainless steel cages. The temperature (24 ± 2 °C) and humidity (60 ± 5 %) of the animal room were kept constant and the rats were kept under a 12-hour light/dark cycle (artificial light from 07:00~19:00). They were acclimated for one week and fed a pelletized regular chow diet. At nine weeks of age, all 47 rats were bilaterally ovariectomized (OVX) under anesthesia with ketamine (50 mg/kg b.w.) and



xylazine (45 mg/kg b.w.). The abdominal area was sterilized with 75 % ethanol and opened by a surgical operation. The uterus and ovaries were taken out, and only the ovary was ligated and cut off. Then, the uterus and adipose tissue were put back into the abdomen and sewn up. The OVX rats were randomly divided into four groups and fed one of four diets: a casein diet without soybean addition (NC group, n = 12), a yellow soybean diet (YS group, n = 12), a black soybean diet (BS group, n = 12), or a sword bean diet (SB group, n = 11) for 10 weeks. The beans were purchased from a local market and autoclaved for 16 minutes at 121 °C

Table I: Compositions of casein, yellow soybean, black soybean and sword bean (g/100 g edible portion). Ingredients

Water

Protein

Casein

0.96

98.3

Yellow soybean2)

9.6

34.4

18.6

28.4

Black soybean3)

11.0

35.2

18.2

26.4

Sword bean4)

10.4

22.7

3.2

52.2

1)

Fat Carbohydrate 0.05

0.63

1)

Lactic Acid Caseins (Nice Ltd., Ukraine) Powdered yellow soybean was autoclaved and dried 3) Powdered black soybean was autoclaved and dried 4) Powdered sword bean was autoclaved and dried

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to decrease their trypsin-inhibiting activity. After cooling, beans were converted to powder using a 60 mesh. Each diet was prepared by mixing various quantities of the powdered beans with the AIN-93M-based diet. The yellow soybean, black soybean, and sword bean powders accounted for 35 %, 35 %, and 50 % of the experimental diet, respectively, to ensure isonitrogeneous contents (15 %). Since each bean has a different protein content (34.4 % for yellow soybean, 35.2 % for black soybean, and 22.7 % for sword bean). Thus, the protein source in the diet was either casein or whole soy powder (Table I). All diets were isonitrogeneous and isocaloric, and the energy ratio of carbohydrates to proteins to lipids was adjusted to be 65:15:20, respectively. All rats received water and food ad libitum. The composition of the normal experimental diet is provided in Table II. During the experimental period, body weight was measured once per week and food intake was measured three times a week. All animals were housed and cared for in accordance with the US National Institutes of Health (NIH) Guide for the Care and Use of Laboratory Animals.

Sample collection

2)

At the end of the experimental period, the rats were deprived of food overnight and sacrificed under ethyl

Table II: Composition of experimental diet (g/kg). Ingredient

NC

YS

Casein

150

Yellow soybeans

BS

350

Black soybeans

350

Sword beans D,L-methionine

SB

500 3

3

3

3

Corn starch

350

240

240

65

Sucrose

300

300

300

300

50

30

30

10

Cellulose Corn oil Mineral Mix

100

30

30

75

1)

35

35

35

35

2)

10

10

10

10

2

2

2

2

Vitamin Mix

Choline bitartrate 1)

AIN-93M mineral mixture AIN-93M vitamin mixture NC: ovariectomized rats fed a casein diet YS: ovariectomized rats fed a yellow soybean diet BS: ovariectomized rats fed a black soybean diet SB: ovariectomized rats fed a sword bean diet 2)


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ether anesthesia. Blood samples were collected immediately into heparin-coated sterile tubes by cardiac puncture. Plasma was obtained from the blood samples by centrifugation (4000 × g for 10 minutes) at 4 °C and stored at –70 °C until further analysis. The livers were removed, washed with cold saline, patted between paper towels, weighed, and then stored at –70 °C for laboratory analysis.

filtration of extracts, the collected solution was centrifuged at 3,000 × g for 10 minutes. The chloroform phase was collected and vacuum-concentrated. Total lipids were estimated by gravimetric analysis. The liver cholesterol concentrations were measured using a commercial diagnostic kit (SIMENSE Germany).

Hepatic antioxidant enzyme activities Plasma lipid profiles The concentrations of triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were measured using a commercial diagnostic kit (SIMENSE Germany Co, UK) and a photometric autoanalyzer (ADVIA 2400, Japan). The TC and TG levels in the plasma were estimated by the COD-POD method and the GK-GPO method, respectively. The HDL-C level in plasma was determined after precipitation of apoB-containing lipoproteins by sodium phosphotungstate and MgCl2. The LDL-C level in plasma was calculated using Friedewald’s formulation [27].

Liver lipid profiles Total lipids in the liver were extracted according to the Folch method [28]. One gram of liver tissue was homogenized with chloroform/methanol (2:1, v/v), and then 2 mL of ice-cold distilled water was added. After

Two grams of liver tissue were homogenized in 10 mL of a 0.25 M sucrose buffer, then the homogenates were centrifuged at 600 × g for 10 minutes to remove the nuclear fraction, and the remaining separated supernatant was centrifuged at 10,000 × g for 20 minutes to collect the mitochondrial fraction for a catalase (CAT) assay. The supernatant was ultracentrifuged at 105,000 × g for 1 hour to isolate the cytosolic fraction for the superoxide dismutase (SOD) assay. SOD activity was estimated according to the method of Marklund and Marklund [29], which uses a color change due to auto-oxidation of pyrogallol. One unit (U) of enzyme activity was calculated as the protein content inhibiting 50 % of the auto-oxidation of pyrogallol without an enzyme source. SOD activity was expressed as U/mg protein. CAT activity was measured by the disappearance rate of H2O2 monitored spectrophotometrically at 240 nm according to the method of Aebi with slight modification [30]. One unit (U) of enzyme activity was defined as the amount of enzyme catalyzing 1 μmol of H2O2 per minute at 25 °C. The CAT activity was expressed as U/mg protein.

Table III: The effects of various bean types on body weight, weight gain, food intake, and liver weight in ovariectomized rats*. Variables

Groups NC

Body weight (g) Initial Final

YS

164.83 ± 2.05NS 322.08 ± 11.69

a

BS

164.66 ± 2.83

SB

164.08 ± 2.78 b

288.75 ± 7.88

163.45 ± 1.42

b

221.40 ± 2.07c

287.25 ± 9.70

Weight gain (g/day)

1.70 ± 0.12a

1.34 ± 0.08b

1.33 ± 0.11b

0.61 ± 0.02c

Food intake (g/day)

12.65 ± 0.33a

11.18 ± 0.19b

11.06 ± 0.35b

9.96 ± 0.05c

2.48 ± 0.11

2.31 ± 0.07

2.25 ± 0.07

Liver weight (g/100 g b.w.)

NS

2.29 ± 0.09

*

Data are expressed as mean ±S.E.M. of 11 to 12 rats per group. Values in the same row with different superscripts (a, b, and c) are significantly different at a p-value less than 0.05 by one-way ANOVA and Duncan’s multiple-range test. NS: Not significant NC: ovariectomized rats fed a casein diet YS: ovariectomized rats fed a yellow soybean diet BS: ovariectomized rats fed a black soybean diet SB: ovariectomized rats fed a sword bean diet Int. J. Vitam. Nutr. Res., 80 (2), 2010, © Hogrefe & Huber Publishers


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Table IV: The effects of various bean types on plasma TG, TC, HDL-C, and LDL-C levels in ovariectomized rats* (mg/dL).. Variables

Groups NC

YS

BS 36.75 ± 1.73

40.72 ± 2.60b

53.36 ± 4.40a

40.33 ± 2.70b

27.50 ± 3.19c

34.54 ± 3.38bc

a

b

c

4.54 ± 0.63bc

54.58 ± 4.79

TC LDL-C

7.83 ± 0.68

HDL-C

9.69 ± 0.54NS

ab

SB

46.58 ± 4.29

TG

a

b

6.50 ± 0.92

3.58 ± 0.65

10.51 ± 0.49

10.30 ± 0.90

11.02 ± 0.62

* Data are expressed as mean ±S.E.M. of 11 to 12 rats per group. Values in the same row with different superscripts (a, b, and c) are significantly different at a p-value less than 0.05 by one-way ANOVA and Duncan’s multiple-range test. NS: Not significant NC: ovariectomized rats fed a casein diet YS: ovariectomized rats fed a yellow soybean diet BS: ovariectomized rats fed a black soybean diet SB: ovariectomized rats fed a sword bean diet

Hepatic thiobarbituric acid reactive substances (TBARS) assay The concentrations of hepatic TBARS were determined using the method of Ohkawa et al. with slight modification [31]. Approximately 0.2 mL of 8.1 % sodium dodecyl sulfate (SDS), 1.5 mL of 20 % acetic acid, 1.5 mL of 0.8 % tert-butyl alcohol (TBA), and 0.6 mL of distilled water were added to 0.2 mL of liver tissue homogenate, and the solution was vortexed. The reaction mixture was placed in a water bath at 95 °C for 1 hour. After cooling, 1.0 mL of distilled water and 5.0 mL of an n-butanol/pyridine mixture (15:1 v/v) were added and the solution was then vortexed. Then, after centrifugation at 800 × g for 10 minutes, the absorbance of the upper layer was measured at 535 nm. The quantity of TBARS is proportionate to the amount of malondialdehyde (MDA), a lipid peroxidation product generated by the oxidation of membrane lipids by reactive oxygen species. The results were expressed as nmol MDA/g liver.

Statistical analysis Experimental results are presented as mean ± SEM and statistical analyses were performed using the SPSS program (Statistical Package for the Social Sciences 12.0). Experimental groups were compared by one-way ANOVA, and the significance of differences between groups was validated by Duncan’s multiplerange test (p < 0.05).

Results There were no significant differences in initial body weight among rats in the four groups (Table III). However, at the end of the experiment, final weight, weight gain, and food intake were the highest in the NC group and the lowest in the SB group. The weights of rats in the YS and BS groups were generally higher than those in the SB group, but were generally lower than those in the NC group. Liver weight per body weight was not significantly different between the various bean groups and normal control group. Accordingly, consumption of the various beans did not influence liver weight. Plasma TG, TC, and LDL-C levels were generally lower in the groups fed a yellow soybean-, black soybean-, or sword bean-supplemented diet than the untreated control group (Table IV). Plasma TG levels were generally lower in the BS and SB groups than in the NC group. Plasma TC and LDL-C levels were generally lower in the various groups fed beans than in the NC group. Notably, both plasma TC and LDL-C levels in the BS group were the lowest among the various bean groups. Plasma HDL-C levels were not significantly different between the various bean groups and NC group, although the various bean groups tended to have higher plasma HDL-C levels than the NC group. Hepatic total lipid and total cholesterol levels were generally lower in the groups fed yellow soybean-, black soybean-, or sword bean-supplemented diets compared with the untreated control group (Table V). Notably, hepatic total lipid levels were generally lower in the YS and SB groups than in the NC group. Hepatic total cholesterol levels were generally lower in the SB groups than in the NC group, while total


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cholesterol levels were not significantly different between the YS and BS groups. Superoxide dismutase (SOD) and catalase (CAT) activities were higher in the groups fed yellow soybean, black soybean, or sword bean than in the untreated control group (Table VI). Notably, SOD activities were generally higher in the YS and BS groups than in the NC group. CAT activity was generally higher in the groups fed various bean types than in the NC group, but there were no significant differences in CAT activity among the various bean-fed groups. Hepatic TBARS levels were lower in the groups fed beans than in the NC group. The SB group, and in particular the BS group, had lower TBARS levels than the NC group.

Discussion We investigated the effects of consumption of three bean types on lipid levels, lipid peroxidation, and antioxidant enzyme activities in ovariectomized rats, an animal model of the postmenopausal condition characterized by ovarian hormone deficiency. The lipid profiles, lipid peroxidation levels, and antioxidant enzyme activities of OVX rats fed a diet supplemented with yellow soybeans, black soybeans, or sword beans were evaluated and compared with those of rats fed a casein diet. The parameters measured above are risk factors for cardiovascular disease, particularly atherosclerosis. Rats in the NC group showed the greatest weight gain and food intake, followed by rats in the YS and BS groups, and finally rats in the SB group. The results of this study indicate that consumption of beans significantly reduced body weight gain and food intake compared to consumption of casein. The lower body

weight gain in rats fed various bean diets is probably due to the lower food intake of these rats compared to rats fed casein diets. In addition to the lowest food intake, the SB group had the lowest body weight gain among the various bean groups. This may be due to a difference in the taste and smell of the SB-supplemented diet compared to the other experimental diets. In previous studies [32, 33], levels of various lipids were significantly higher in OVX rats than in shamoperated rats. In fact, because of the possibility that an ovariectomy might in itself increase the levels of various lipids, we did not include a sham group in our study. In this study, rats fed various bean types showed a decrease in plasma TG, TC, and LDL-C levels compared with the NC group. Plasma TG levels in the BS and SB groups were significantly lower than in the NC group. Both plasma TC and LDL-C levels in the groups fed beans were significantly lower than those in the NC group. Notably, the BS group had the lowest plasma TC and LDL-C levels among the various bean-fed groups. Hepatic total lipid and total cholesterol levels were also significantly lower in the various bean groups than in the NC group. Notably, hepatic total lipid levels were significantly lower in the YS and SB groups, and hepatic total cholesterol levels were significantly lower in the SB group, than the NC group. Sirtori et al. [34] and Descovich et al. [35] found that diets high in soy protein (all animal protein replaced) substantially reduced blood LDL cholesterol by 20~30 % in animals with severe hypercholesterolemia. When soy protein is substituted for animal protein, hypercholesterolemia does not occur. Thus, either casein diets have a direct hypercholesterolemic action, or soy protein diets have a cholesterol-lowering action. In our study, consumption of various beans resulted in a decrease in levels of TG, TC, and LDLC. The soy protein contents of the experimental diets

Table V: The effects of various bean types on hepatic lipid profiles in ovariectomized rats*. Variables

Lipid profiles (mg/g wet liver) Total lipids Total cholesterol

Groups NC

YS

BS

SB

50.87 ± 9.07a 4.84 ± 0.21a

32.83 ± 2.37b 4.53 ± 0.20ab

40.49 ± 3.75ab 4.65 ± 0.16ab

29.88 ± 2.79b 4.16 ± 0.17b

* Data are expressed as mean ± S.E.M. of 11 to 12 rats per group. Values in the same row with different superscripts (a, b, and c) are significantly different at a p-value less than 0.05 by one-way ANOVA and Duncan’s multiple-range test. NS: Not significant NC: ovariectomized rats fed a casein diet YS: ovariectomized rats fed a yellow soybean diet BS: ovariectomized rats fed a black soybean diet SB: ovariectomized rats fed a sword bean diet



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Table VI: The effects of various bean types on hepatic SOD and CAT activity and TBARS levels in ovariectomized rats*. variables

Groups NC

YS

BS

Antioxidant status SOD (U/mg protein)

3.44 ± 0.05b

3.82 ± 0.06a

3.82 ± 0.13 a

CAT (U/mg protein)

22.75 ± 0.48b

26.87 ± 1.08a

30.10 ± 1.25a

Oxidant status TBARS (nmol/g wet liver)

8.53 ± 0.49a

7.12 ± 0.33ab

5.10 ± 0.60c

SB 3.59 ± 0.05ab 28.23 ± 1.78a 6.29 ± 0.49bc

*

Data are expressed as mean ± S.E.M. of 11 to 12 rats per group. Values in the same row with different superscripts (a, b, and c) are significantly different at a p-value less than 0.05 by one-way ANOVA and Duncan’s multiple-range test. NC: ovariectomized rats fed a casein diet YS: ovariectomized rats fed a yellow soybean diet BS: ovariectomized rats fed a black soybean diet SB: ovariectomized rats fed a sword bean diet

were the same (15 %) and the isoflavone contents of the experimental beans were similar (0.25 % for yellow soybean, 0.27 % for black soybean, and 0.22 % for sword bean). Postmenopausal women are generally at higher risk for cardiovascular disease because ovarian hormone deficiency is associated with elevated levels of circulating TC and LDL-C. In previous studies, dietary supplementation with soybean isoflavones significantly decreased plasma TC, TG, and especially LDL-C levels, and significantly increased HDL-C levels [36]. We hypothesize that the various isoflavone-containing beans investigated in this study may have lowered plasma cholesterol levels by their estrogenic activity. However, this hypocholesterolemic effect is not simply an estrogenic effect, because soybeans are also rich in anthocyanins and other phytochemicals. Anthocyanins play important roles as dietary antioxidants in the prevention of oxidative damage, and can reduce the risk of coronary heart disease [37,38]. Black soybeans have a stronger anti-oxidative effect than yellow soybeans and sword beans. The anti-oxidative activity of dark-colored soybeans may be higher than those of light-colored soybeans [39]. In our study, the rats fed BS had lower plasma TG, TC, and LDL-C levels than the rats fed YS or SB. Although the different beans had similar isoflavone and soy protein contents, the differential result may be because the BS seed coat contains higher quantities of anthocyanins than the SB and YS seed coats. LDL oxidation is one of the more well-studied free radical-mediated processes. Oxidized LDL is responsible for the pathogenesis of atherosclerosis that can lead to the build-up of plaque in arteries [40]. Therefore, consumption of food rich in antioxidants may protect against cardiovascular disease. Anthocyanins in BS appear to contribute to

the reduction in lipids observed after the consumption of BS. Although the cholesterol-lowering effects of soybeans are widely accepted, the mechanism(s) underlying these effects is not well understood, but is postulated to be due to soy proteins, isoflavones, and anthocyanins, as well as other components [9, 13]. In addition, soybeans contain a wide range of phytochemicals that are currently being investigated. It is possible that the various phytochemicals interact synergistically to lower cholesterol. Our results suggest that consumption of various types of beans, namely soybeans and sword beans, has a beneficial effect on lipid profiles in OVX rats, as indicated by decreased TG, TC, and LDL-C levels in both the blood and liver. Antioxidant enzymes such as SOD and CAT can effectively convert superoxide radicals to molecular H2O2 and oxygen, and can consecutively decompose H2O2 to molecular water and oxygen [41]. In fact, CAT and SOD are capable of eliminating lipid peroxidation products and reactive oxygen species (ROS), thereby directly protecting cells and tissues from deleterious radicals [42]. Ozgocmen et al. [43] reported that postmenopausal women appeared to have increased oxidative stress as evidenced by high MDA levels and low CAT activity, suggesting that lack of estrogen had a pro-oxidant effect due to an increase in free radical formation. Increased oxidative stress and reduced bioavailability of antioxidants may induce oxidative damage in postmenopausal woman and OVX rats. In this study, SOD and CAT activities were higher in the groups fed various types of beans than the NC group. Our results are consistent with previous studies that demonstrated that various types of beans had antioxidant capacity both in vivo and in vitro [44, 45]. The protective roles of various beans against oxidative damage


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in OVX rats might be due to their ability to decrease lipid oxidation, as it is known that isoflavones have antioxidant activity [46]. However, SOD and CAT activities were not significantly different between the bean-fed groups in our study. Phytochemicals may act by different mechanisms to defend against harmful free radicals. Recently, soybeans have attracted attention because of their strong antioxidant, anti-cancer, and anti-inflammation effects [26]. Based on these results, we hypothesize that consumption of sword bean as well as yellow soybean and black soybean can increase the activities of antioxidant enzymes in postmenopausal women. Further studies are needed to confirm this hypothesis. Hepatic TBARS levels are commonly used to assess lipid peroxidation and oxidative stress [47]. In this study, hepatic TBARS levels were the lowest in the BS group, followed by the SB and YS groups, and highest in the NC group. Soy isoflavones can directly quench free radicals, though they may also decrease oxidative damage through indirect mechanisms such as induction of cellular antioxidant- scavenging enzymes [48]. The different hepatic TBARS levels in rats fed various types of bean may be due to the different levels of isoflavones and anthocyanins in the beans. Notably, the strong effect of black soybean on hepatic TBARS levels may be related to the high anthocyanin content of this type of bean. Anthocyanins may prevent the copperinduced oxidation of LDL by both metal-chelating and radical scavenging mechanisms [49]. Kowalczyk et al. [50] demonstrated that anthocyanin supplementation decreased hepatic TBARS levels and increased antioxidant activity in animals. Oxidative stress is associated with cholesterol accumulation and foam cell formation, which are the hallmarks of early atherosclerosis in vascular tracts [51]. Anthocyanins can thus protect against oxidative damage and reduce the risk of coronary heart disease [52]. Overall, consumption of various beans had a beneficial effect on antioxidant enzyme activities in OVX rats, as indicated by increased SOD and CAT activities, and by decreased TBARS levels. In conclusion, our results suggest that consumption of beans containing soy protein and various antioxidant micronutrients may inhibit oxidative stress in postmenopausal women by enhancing antioxidant activity and decreasing levels of harmful lipids. These effects are likely to be mediated by soy proteins, isoflavones, anthocyanins, and other phytochemicals present in these beans. Notably, intake of black soybeans, which contain the highest anthocyanin levels, resulted in the greatest improvement in risk factors associated with atherosclerosis and cardiovascular disease. Furthermore, sword beans as well as yellow and black

soybeans may protect against cardiovascular disease and atherosclerosis. Further studies are required to determine the potential implications of the consumption of sword beans on lipid metabolism.

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Department of Food & Nutrition Hanyang University, #17 Haengdang-dong Seongdong-gu Seoul 133 – 791 South Korea Telephone: +82–2-2220–1206 Fax: +82–2-2281–8285 E-mail: [email protected]
