Protective Effects of Rice Bran on Chemically Induced Colon Tumorigenesis may be Due to Synergistic/Additive Properties of Bioactive Components
In this study we examined the preventive properties of Rice Bran (RB) and germ on the incidence of azoxymethane induced colon tumorigenesis in Fisher 344 male rats. We also examined the cytotoxic and apoptotic properties of RB using an in vivo model. Tumor incidence (%) in C and RB 5% and RB 10% were 100, 55 and 64, respectively. Tumors/tumor Bearing Rats (TBR) were 3.8, 2 and 1.56 for C, RB 5% and RB 10%, respectively. Tumor size (mm) was larger in control (6.50) than in rats fed RB 5% and RB 10% (1.33 and 0.64). After 12, 24 and 48 h of incubation with RB extracts, LDH (%) release ranged from 2.25-46.79. Present results suggest that feeding RB at 5 and 10% levels significantly (p<0.05) reduced the incidence of AOM induced colon tumors in Fisher 344 male rats. We conclude that the protective effects of RB against colon tumorigenesis may possibly be attributed to the synergistic/additive actions of phytochemicals contained in RB.
to cite this article:
J. Boateng, M. Verghese, V. Panala, L.T. Walker and L. Shackelford, 2009. Protective Effects of Rice Bran on Chemically Induced Colon Tumorigenesis may be Due to Synergistic/Additive Properties of Bioactive Components. International Journal of Cancer Research, 5: 153-166.
Despite efforts focused on chemoprevention, colon cancer still remains the
second leading cause of cancer deaths in the Unites States (American
Cancer Society, 2008).
Diet plays a major role in both the prevention and onset of many chronic diseases such as cancer, cardiovascular diseases (CVD) and diabetes. Diets derived primarily from edible plant sources such as grains and cereals are beneficial for the prevention of diseases and maintenance of good health.
Dietary fiber is one of the most important sources of non-nutritive compounds
that provide the potential of preventing chronic diseases. Numerous data have
shown the importance of dietary fiber in improving levels of blood cholesterol,
cardiovascular diseases (CVD), diabetes and cancers of the gastro-intestinal
tract (Reddy, 1999; Levi et al.,
2001; Peters et al., 2003; Mahadevamma
et al., 2004). Although, there are a wide range of terms, dietary
fiber originates mostly from plant sources such as fruits, vegetables, legumes
and cereals; and is thus defined as the cell wall polysaccharides of plants
that cannot be hydrolyzed by the human digestive system (Harris
and Ferguson, 1993; Ferguson and Harris, 1996).
Besides plant cell wall components such as cellulose, pectin and lignin, dietary
fibers encompass resistant starches, oligosaccharides and non-starch polysaccharides
such as seaweeds (e.g., gums and mucilages) (Coudray et
Despite its health promoting capabilities, dietary fiber is classified as soluble
or insoluble which according to Coudray et al. (2002)
reflects the different physiochemical properties and their abilities to produce
different biological effects. Among the numerous sources of dietary fibers,
cereal brans are the most studied and their protective effects against diseases
is noteworthy. One of the cereals of particular interest is rice. Rice is one
of the most important cereal crops that is a staple for a majority of the worlds
population (Bird et al., 2000). When rice undergoes
the milling process to remove the bran, almost all of its nutrients, i.e., minerals
and vitamins are lost along with the bran.
Besides providing protein and minerals, rice bran is an excellent source of
vitamin B and E, especially tocotrienols. It also contains polyphenolic compounds
that have been shown to interfere with the proliferation or colony-forming ability
of breast or colon cells (Hudson et al., 2000).
Harris et al. (1998) stated that while different
cereal bran species appears to have different protective effects when exposed
to carcinogens, rice bran when compared to oat and barley brans has a superior
protective effect. While many foods contain several disease fighting components,
some such as rice bran posses novel constituents such as tocotrienols,
sitosterol ferulate, cycloartenol ferulate and gamma-oryzanol that have antioxidative
and antigenotoxic activities (Yasukawa et al., 1998;
Hudson et al., 2000; Nam
et al., 2005). Other phenolic constituents such as phytic acid was
shown to exhibit anticancer properties through the regulation of vital cellular
functions such as signal transduction, cell proliferation and differentiation
(Vucenik and Shamsuddin, 2006). The bio active components
of rice bran, sitosterol ferulate, 24-methylcholesterol ferulate, cycloartenol
ferulate and 24-methylenecycloartanol ferulate were shown to inhibit 12-O-tetradecanoylphorbol-13-acetate
(TPA)-induced inflammation in mice (Yasukawa et al.,
Despite the fact that rice bran is abundantly produced in the rice milling industry, it is still underutilized and is yet to gain recognition as an excellent source of phytonutrients with health promoting properties. As such, there is a need to explore it beneficial uses, especially as it relates to health.
Azoxymethane (AOM), a metabolite of 1, 2-Dimethylhydrazine (DMH) an organotropic
colon carcinogen has been extensively used to induce colon carcinogenesis in
susceptible laboratory animals (Papanikolaou et al.,
1998; Dommels et al., 2003). The AOM is generally
preferred to DMH because it is a more potent carcinogen than DMH based on molarity
and has an enhanced chemical stability in solutions (Papanikolaou
et al., 1998). Most studies have reported that two successive injections
of AOM, 1 week apart, are adequate in inducing colon cancer in rats. Induction
by AOM is the most popular experimental model often used to identify dietary
modulations of colon cancer (Dommels et al., 2003).
Based on these observations, we examined the putative effects of Rice Bran (RB) with germ on azoxymethane (AOM) induced colon carcinogenesis in Fisher 344 male rats. We also determined the cytotoxic and antiproliferative effects of RB extracts in CaCo-2 colon cells.
MATERIALS AND METHODS
Animal Housing and Diets
After a one week period of acclimatization a total of 42 Fisher 344 male
weanling rats (3-4 weeks old) (Harlan, IN) were assigned to 3 groups (Fig.
1). The Rats in the end point study were initially fed AIN-93G (Reeves
et al., 1993a, b) as control (C) and AIN-93G
+5% and 10% RB (The RiceX company, Phoenix, AZ) diets (Table 1)
and switched to AIN-93M at 20 weeks of age until the end of the study. Relative
humidity and temperature were maintained at 50% and 21±1°C, respectively
and dark and light cycles were held at 12 h intervals. Body weights were recorded
every two weeks and daily feed intake was recorded. Diets were prepared biweekly
and kept at 4°C for freshness. Ingredients for preparation AIN-93 diets
were obtained from ICN (Costa Mesa, CA). The study was conducted at Alabama
A and M University Food and Animal Sciences Department in July, 2007 and all
protocols involving rats were approved by the Institutional Animal Care and
Use committee of Alabama A and M University.
||Schematic representation of feeding (a) control and (b) RB
diets in EPT study. Scale is not proportional, Control diet is based on
AIN-93G/M (Reeves et al., 1993a, b).
Rice bran was fed at 5 and 10% levels, EPT: End point tumor
of dietsa in experiment
|Formulations of diets based on AIN-93G (American Institute
of Nutrition, Reeves et al., 1993a, b);
aExperimental diets: C-control; RB-rice bran. bCommon
ingredients (g): dextrose, 132; mineral mix (AIN-93G), 35; vitamin mix,
10; L-cystein, 3; choline bitatrate, 2.5
Aom Injection and Sample Collection
To induce ACF and colon tumors all animals except saline controls received
2 subcutaneous injections of azoxymethane (Sigma Chemicals, St. Louis, MO) at
7 and 8 weeks of age. The AOM was administered in saline at 16 mg kg-1
body. Rats were killed by CO2 asphyxiation at 17 and 45 weeks of
age and colons were removed and flushed with potassium phosphate buffer (0.1
mol L-1, pH 7.2) and prepared for counting tumors. Colons were removed
for ACF enumeration and liver samples and colonic mucosal scrapings were collected
and stored at -80°C until analysis for Glutathione-S-Transferase (GST) activity.
Cecum of rats was weighed and pH of cecal contents was noted.
Enumeration of Aberrant Crypt Foci (ACF)
Colons of rats from each group were flushed with PBS (0.1 M, pH 7.2) and
ACF and crypts per focus were enumerated as described by Bird
Characterization of Colon Tumors
Colon tumors were collected and characterized as described by Shackelford
et al. (1983), according to size, location, number and tumors per
Tumor Bearing Rat (TBR).
Preparation of Liver and Colonic Tissues for Glutathione-s-Transferase (GST)
The GST activity in rat liver cytosol and colonic mucosal scrapings was
assayed following the methods described by Habig et al.
(1974). Briefly, 1 g of tissue sample was homogenized in 10 mL of potassium
phosphate buffer (0.1 M, pH 7.2) and centrifuged at 10,000 rpm for 30 min. The
clear supernatant was mixed with 1, chloro2, 4-dinitrobenzene (CDNB) (Fisher
Scientific, Suwannee, GA), potassium phosphate buffer and glutathione reductase
(Sigma chemicals, St. Louis, MO). One unit of GST activity is expressed as the
amount of enzyme required to conjugate 1 μmole of CDNB with GSH per minute.
The resulting product was analyzed using a UV/VIS dual beam spectrophotometer
(Cary1/3, Varian) at 340 nm.
Preparation of Rice Bran Extracts
Defatted rice bran was extracted with 80% methanol (v/v) (at 1:10 ratio)
for approximately 12 h at ambient temperature. The methanolic extracts were
then filtered through Whatman No. 2 paper to remove residue. The filtrates were
concentrated under restricted light using rotary evaporation (40°C) and
the phenolic concentrate was made to a final volume of 10 mL with distilled
water. The crude Rice Bran (RB) extracts were immediately stored at -80°C
after flashing with nitrogen gas.
Cell Culture Experiment
CaCo-2 cells were purchased from American Type Culture Collection (ATCC,
Mannasas,VA) and maintained in Dulbeccos Modified Eagles Medium
(DMEM) with 10% Fetal Bovine Serum (FBS) and 1.0 mM sodium pyruvate. Cells were
incubated at 37°C, 5% CO2 until confluent (70-90%). For experiments,
cells were seeded in 12 well tissue culture plates at a density of 3.28x105.
Cells were incubated as previously specified until a monolayer developed. After
the development of a monolayer (70-80% confluence), cells were rinsed twice
with PBS and incubated for 24 and 48 h with 800 μL of fresh media (serum
free) containing different concentrations (0-1000 μg mL-1) of
rice bran extracts. Serum free media containing no RB extracts served as control.
After indicated incubation times, the culture supernatant was removed and used
to assess lactate dehydrogenase (LDH) (EC 22.214.171.124).
Cytotoxicity of RB was measured by the release of LDH from the CaCo-2 cells
into the culture supernatant. The LDH release was quantified using a calorimetric
cytotoxicity detection kit (LDH) (Roche Diagnostics, Indianapolis, IN) according
to the manufacturers instructions. Assay was performed in triplicate.
MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5 Diphenyltetrazolium Bromide) Assay
Cell viability was measured using an MTT assay kit (Roche Diagnostics, Indianapolis,
IN). Briefly, Caco-2 cells were seeded at a density of 1.2x104 cells
well-1 into a 96-well plate in final volume of 100 μL of media.
After 24 h post seeding, the cells were exposed to different concentrations
of RB (0-1000 μg mL-1) and maintained in culture for 24 and
48 h at 37°C in a humidified atmosphere containing 5% CO2. After
treatment, the cells were incubated for 3 h at 37°C with a solution of MTT
following manufacturers instructions. The absorbance of the reduced intracellular
formazan product was read at 550/630 nm on a synergy HT micro plate reader.
Each assay was performed in triplicate.
Data from three experiments were combined (cell culture study) and analyzed
using the SAS(2007). Results were performed by ANOVA and
values are given as Means±SEM. Means were separated using Tukeys
studentized range test. Differences between treatment groups were tested by
students t test and paired t test. Unless otherwise indicated the level
of significance was considered significant at p<0.05.
Body Weight Gain, Feed Intake and Cecal Weight and pH
Although, daily feed intake was similar in the treatment groups in the ACF
study, weight gain in rats fed Rice Bran (RB) was significantly (p<0.05)
lower compared to rats fed the control (Table 2). We detected
a 7 and 15% decrease in weight gain compared to the control. In the EPT study
however, feed intake in the rats fed 10% RB was significantly (p≤0.05) higher
compared to the rats fed 5% RB and the control group. Even though daily feed
intake and weight gain in rats fed RB was significantly (p≤0.05) higher compared
to the control group, among the rats fed RB, the group given 5% RB weighed significantly
(p≤0.05) more than the group fed 10% RB. Overall weight gain was 34 and 18%
higher in the rats fed RB at 5 and 10%, respectively, compared to the control.
In both the ACF and EPT studies, cecal weight in rats fed 10% RB was significantly
(p≤0.05) higher than in rats fed 5% RB and the control. The cecum was nearly
twice as large in the 10% RB fed rats compared to the control and over 30% larger
than their 5% counterparts. Since, cecal pH is inversely proportional to cecal
weight, cecal pH was seen to be significantly (p≤0.05) lower in 10% RB fed
Aberrant Crypt Foci (ACF), Total Colonic Aberrant Crypts and Crypt Multiplicity
The ACF incidences in rats fed experimental diets are shown in Table
3. As detected, ACF in the distal colon were significantly (p<0.05) higher
compare to distal colons in all the experimental groups.
gain, feed intake, cecal weight and cecal pH in Fisher 344 male rats
|Values are Means±SEM, *n = 4. abMeans in
a row with the same superscript do not significantly differ (p<0.05)
using Tukeys studentized test. RB: Rice bran
of aberrant crypt foci in colon of azoxymethane-induced Fisher 344 male
|Values are expressed as means±SEM; n = 4; abcMeans
in the same column with the same letter(s) are not significantly different
by Tukeys studentized range test (p≤0.05); RB: Rice bran
While there were no significant differences in the number of ACF in the proximal
colons of rats fed the lower dose RB (i.e., 5%) and the control, ACFs were decreased
by approximately 45% when compared to the group fed 10% RB. In the distal colon
ACF were significantly (p<0.05) lower in the treatment groups compared to
the control with reductions of 57 and 66%, respectively. Overall total number
of ACF developed in the treatment groups were decreased by 44 and 61%, respectively.
Similarly, total aberrant crypts/colon was significantly (p<0.05) lower in
the treatment groups compared to the control with decreases of 55 and 71%, respectively
(Table 4). Among the treatment groups we detected 30% and
35% reductions in total ACFs and total aberrant crypts/colon, respectively,
when rats were fed 10% compared to 5% RB. Crypt multiplicity is crucial when
using ACF as a colon cancer biomarker. ACF consisting of four or more crypts
has been reported as putative premalignant lesions for colon cancer development
(Seraj et al., 1997). In this study we noted
that crypt multiplicity, especially aberrant crypts with 3, 4 and ≥5 foci
was significantly (p<0.05) lower in the groups fed RB compared to the control
(Fig. 2). The ACF with ≥3 crypts were predominantly seen
in the distal colon.
Distal and Proximal Tumors
All the rats fed the control diet developed tumors compared to 54 and 64%
in the groups fed RB at 5 and 10%, respectively (Table 5).
While there were no tumors in the proximal colon in rats fed 10% RB, there was
55% incidence of proximal tumors in the 5% RB fed group. There was however,
100% tumor incidence in the distal colon of all rats. Earlier studies have shown
that distal segments of the colon had significantly higher numbers of tumors
than the proximal segments (Verghese et al., 2002a).
Tumors/Tumor-Bearing Rat Ratios (TBR) and Tumor Size
The total number of tumors in the proximal and distal colon in the control
group was significantly (p<0.05) higher compared to the rats fed RB. The
RB fed rats had a 75% reduction in the total number of tumors/rat (Table
6). The number of tumors/rat in the distal colon was significantly higher
than the proximal colon in all the experimental groups. Distal tumors/rat was
approximately 74 and 65% lower in rats fed 5% RB and 10% RB, respectively compared
to the control.
Crypt Foci (ACF) and total crypts in Fisher 344 male rats
|Values are expressed as Means±SEM; n = 4; abcMeans
in a row similar superscripts are not significantly different by Tukeys
studentized range test (p≤0.05); RB: Rice bran
||Rice bran meal on crypt multiplicity in Fisher 344 male rat,
abc Bars without a common letter significantly differ (p<0.05)
using Tukeys studentized range test, RB: Rice bran
incidence (%) of colon tumors in Fisher 344 male rats
|N1 represents the number of rats with tumors; N2
is total number of rats at the end of the experiment; RB: Rice bran
and characterization of AOM induced colon tumors in Fisher 344 male rats
|Values are Means±SEM, abMeans in a column
with the same letter(s) do not significantly differ (p<0.05) using Tukeys
studentized test. N1 represents the number of rats with tumors;
N2 is total number of rats at the end of the experiment. RB:
(GST) activity in rats
|Values are expressed as Means±SEM. abMeans
in the same column with the same letter are not significantly different
by Tukeys studentized range test (p≤0.05). CMS: Colonic mucosal
scrapings, RB: Rice bran
Tumor size (mm)/rat were over six and ten times larger in the control (6.50)
compared to the rats fed 5% RB (1.1) and 10% RB (0.64), respectively. Tumors/tumor
Bearing Rat Ratio (TBR) was significantly (p≤0.05) lower in the rats fed
RB compared to the control (Table 6). The 5% RB fed rats had
a 47% reduction in TBR value, while the rats fed 10% RB exhibited the greatest
reduction in TBR (65%) compared to the control.
Total Glutathione-S-Transferase (GST) Activity
The GST (μmol mg-1 protein) activity in the liver of rats
fed RB in the ACF and EPT studies were significantly (p≤0.05) higher compared
to the control (Table 7). Residual GST activity in the Colonic
Mucosal Scrapings (CMS) was also higher in the rats fed RB (6.2 and 5.84 for
5 and 10% RB) compared with those fed control (3.14). The GST activity in the
hepatic tissue was higher compared to CMS, this is because the liver is the
primary site for detoxification.
LDH Cell Viability Assay
The LDH release which represents cytotoxic effects on the cells corresponding
to total cell lysis is shown in Fig. 3. Present study showed
that LDH release as assessed in the cell culture medium after exposure to RB
extracts following incubation for 12, 24 and 48 h was significantly (p<0.05)
increased with increasing order of concentration. LDH release (%) ranged from
a low of 2.25 (50 μg mL-1) to a high of 46.79% (800 μg
mL-1). The highest release (46.79%) of LDH was seen after 48 h at
all concentrations. The results also showed a dose dependant increase in LDH
release when cells were exposed to RB extracts for 12 and 24 h.
||LDH release in CaCo-2 cells after addition of different concentrations
of RB extracts (50-800 μg mL-1). Data are presented as Means±SEM
of three replicates (p<0.05) using Tukeys studentized test
||The MTT in CaCo-2 cells after addition of different concentrations
of RB extracts (50-800 μg mL-1). Data are presented as Means±SEM
of three replicates (p<0.05) using Tukeys studentized test
Cell Proliferation Using 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium
Bromide (MTT) Reduction Assay
To evaluate the effects of RB extracts on cell proliferation, CaCo-2 cells
were cultured in RB-supplemented media (Fig. 4). The results
indicated that RB extracts at all the concentrations tested inhibited CaCo-2
cell proliferation. Antiproliferative effects of RB extracts against CaCo-2
cells from decreasing order of concentration ranged from 0.51-0.92, 0.37-0.70
and 0.29-0.52 after 12, 24 and 48 h incubation.
The aim of this study was to determine the effects of Rice Bran (RB) with germ
at 5 and 10% levels on AOM induced colon cancer in Fisher 344 male rats. Present
results clearly indicate that rice bran reduced the number of ACF and colon
tumors in Fisher 344 rats. One of the mechanisms associated with the observed
results may be that the dietary fiber in rice bran which is slowly fermented
may exert its protective effects through physical dilution of gut contents,
by its dilution potential and fecal bulking capacity (Ferguson
and Harris, 1996; Zoran et al., 1997). This
property is thought to shorten transit time, thus leading to alterations in
the mutagenicity of intestinal contents, mucosal cytokinetics and the subsequent
effects on excretion of putative carcinogens (Ferguson and
Another aspect to consider is the production of butyrate. Butyrate regardless
of the fiber source is linked with protection against the initial stages of
colon carcinogenesis (Perrin et al., 2001). The
primary function of butyrate is its ability to arrest the growth of neoplastic
colonocytes and inhibit the preneoplastic hyperproliferation induced by some
tumor initiators and promoters (Velasquez et al.,
1996; Dongowski and Proll, 2002).
Rice bran contains several components that may have contributed to the reduction
in numbers of tumors seen in this study. Phytic Acid (PA), which is one of the
constituents in rice bran, is a negatively charged molecule capable of binding
proteins and starch (Rickard and Thompson, 1998). This
leads to their reduced absorption and as a result increases fecal bulk (Rickard
and Thompson, 1998).
The number of ACF in the distal colon has been found to be associated with
markers of fermentation in the cecum, including SCFA and ATP concentration.
Although, we observed a reduced incidence of ACF and tumors in the proximal
compared to the distal colon in the RB fed groups compared to the control, rats
fed rice bran also had significantly (p≤0.05) lower numbers of ACF and tumors
in the distal colon compared to the control group. In some studies (Topping
et al., 1997; Muir et al., 1998, 2004),
fine fibers or some Resistant Starches (RS) were shown to ferment in the proximal
region of the colon, while coarser fibers shifted the site of fermentation further
down to the distal colon. On the other hand in humans or in rodents that have
been experimentally induced with a chemical carcinogen, colon tumors appeared
in the distal portions of the colon (Bufill, 1990; Holt
et al., 1996; Henningsson et al., 2002).
Magnuson et al. (2000) also reported that Fisher
344 male rats that received two successive AOM injections at 15 mg kg-1
s.c.-1 beginning at 7 weeks of age developed tumors in distal portion
of the colon.
In the EPT study, rats consuming 5% RB weighed significantly (p≤0.05) more
and consumed similar amount of feed as the control. The control rats had a greater
tumor burden compared to the RB fed groups and this may have caused malabsorption
of nutrients leading to lower weight gain. Also, the increased energy available
to this group could be as a result of the production of SCFA. In a study Zoran
et al. (1997) postulated that luminal acetate and a large proportion
of propionate, which is not used by the colonic epithelial cells, is transported
to the liver and metabolized or utilized in lipid synthesis. We noted that weight
gain in 10% RB fed rats was similar to the control. This may be due to the satiety
effects associated with cereals rich in fiber. Furthermore, the intake of diets
high in fiber decreases the intake of energy. Previous studies have shown a
positive correlation between high-energy intakes and cancer risk (Andersson
et al., 1996; Furberg and Thune, 2003; Slattery
et al., 2005).
Present results showed a positive correlation between a lower cecal pH and
reduction in ACF and tumor formation. Low pH, which results from fermentation
of dietary fiber resulting in the production of Short Chain Fatty Acids (SCFA),
is believed to prevent the overgrowth of pH-sensitive pathogenic bacteria. Earlier
studies on other dietary fiber sources have indicated that the major genera
of colonic bacteria, Bifidobacterium and Lactobacillus are generally not pathogenic.
These organisms augment resistance to disease by reducing pathogenic and putrefactive
bacteria by lowering pH (Keenan et al., 2006).
Consequently, these organisms contribute to the stabilization of the microflora
and ultimately to the health of the host. An acidic cecal pH is indicative of
fecal pH reduction and fecal pH has been suggested to be a possible factor in
suppression of colon tumorigenesis (Verghese et al.,
In the current study feeding RB at 5 and 10% levels resulted in 43 and 60%
reductions in ACF study and in the EPT study by 47 and 65%, respectively. However,
Kawakawa et al. (1999) reported 20% reduction
in ACF in rats fed 2.5% rice germ. The authors also showed reductions of 28
and 46% when rats were fed 2.5% rice germ and gamma-aminobutyric acid (GABA)-enriched
defatted rice-germ. It is possible that the increased reductions in ACF and
tumors observed in our study are a result of the increased dosage of RB that
was fed to the rats. In addition, the RB used in this study contained equal
mixtures of the bran and germ which may also have contributed to the tumor inhibitory
To our knowledge, we show for the first time the effect of feeding rice bran
on phase II enzyme (GST) activity. Present results indicated an increase in
GST activity in rats fed RB based diets. The ability of butyrate, a byproduct
from fermentation of dietary fiber which has been reported to increase phase
II detoxifying enzymes such as glutathione S-transferase (GST) (Beyer-Sehlmeyer
et al., 2003; Knoll et al., 2005) may
have contributed to the detoxification of dietary carcinogens. Induction of
GST is one of the chemopreventive effects of phytochemicals (Jung
et al., 2006).
It is evident based on present results that the protective effects of grains such as rice bran on colon cancer might be attributed to the presence of dietary constituents other than fiber or antioxidants in these foods. Since, we cannot make the conjecture that the underlying reason for the reduced numbers of colon tumors in Fisher 344 rats may be attributed to fiber, it is possible to assume however, based on earlier studies that other agents besides fiber, may contribute to the antiproliferative, antioxidative and apoptotic activities of rice bran. Rice bran contains components such as fiber, polyphenols, phytic acid ferulic acid, oryzanols and other nutrients, the synergistic/additive effects of these compounds may have led to the enhanced increase in the chemopreventive effects seen in this study.
Lactate dehydrogenase (LDH) release assay and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay are the most commonly used indicators for quantitating cell viability and proliferation. The conversion of actively respiring cells, through a redox activity, converts water-soluble MTT into insoluble purple-colored MTT formazan. After solubilization a decrease in cellular MTT reduction could be an index of cell damage. On the other hand, LDH assay measures the release of the intracellular enzyme LDH upon damage of the plasma membrane and an increase in LDH release could be an index of cell damage.
Present study is one of a handful of studies to show the cytotoxic and antiproliferative
properties of rice bran and germ extracts on colon cancer cell line CaCo-2.
We detected cytotoxic and antiproliferative effects of RB extracts as measured
by percentage LDH release and MTT against CaCo-2 cells after exposure periods
of 12, 24 and 48 h in a dose-dependent and time-dependent manner. In a earlier
experiment we showed the cytotoxic effect of Kidney Bean (KB) extracts against
CaCo-2 cells (Boateng et al., 2008) and attributed
the effect to constituents of KB such as flavonoids which have been reported
to induce apoptosis in cancer cell lines (Paschka et al.,
1998; Yang et al., 1998; Shen
et al., 2003). Crude extracts from black Jamapa bean showed cytotoxic
effect toward HeLa cells (Aparicio-Fernandez et al.,
2006). According to the authors, the cytotoxic effect of crude extract on
HeLa cells may not be due to a single polyphenolic compound in the complex extract
but to the sum of effects from different flavonoids in beans. In another study,
Giron-Calle et al. (2004) found that different
chickpea fractions had both cell growth-promoting and cell growth-inhibiting
affects properties against CaCo-2 cell lines. Present data suggests that bioactive
components present in RB extracts may be attributed for their possible anti-cancer
effect. However, further studies are necessary before any definitive mechanisms
can be recommended.
The present findings suggest that RB extracts exhibited antiproliferative properties in a dose dependant manner in CaCo-2 cells. Present results also showed significant antiproliferative activity with longer incubation periods. The RB extracts contain a mixture of polyphenolic compounds which display multiple effects (synergistic or antagonistic), thus giving its bifunctional properties (cytotoxic and antiproliferative activities). In view of recent data it can be suggested that RB might have antitumor potential and that its possible role in the prevention of cancer warrants further investigations.
Since, rice bran is not widely consumed, the results of this study may provide the impetus for further research can enhance the utilization of rice bran in various nutritional formulas to promote gastro-intestinal health through alteration of gut microbiota. Rice bran can also be used in several baked and Ready to Eat (RTE) products and can also be used as a value added ingredient in meats, smoothies and infant weanling foods.
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Aparicio-Fernandez, X., T. Garcia-Gasca, G.G. Yousef, M.A. Lila, E.G. de Mejia and G. Loarca-Pina, 2006. Chemopreventive activity of polyphenolics from black Jamapa bean (Phaseolus vulgaris L.) on hela and hacat cells. J. Agric. Food Chem., 54: 2116-2122.
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