Potency of Bioactive Compound of Rice Bran for Colon Cancer Prevention

Colon cancer is the second leading cause of death in the world. Bioactive compounds in rice bran have a very active role as antiproliferation of colon cancer cells such as ferulic acid, p-coumaric acid, caffeic acid, gallic acid, protocatechuic acid, sinapic acid, tricin, luteolin, apigenin, myrecitin, rutin, isorhamnetin, γ-oryzanol, γ-tocopherol, δ-tocopherol, γ-tocotrienol, β-sitosterol, phytic acid, and hemicellulose. Mechanism of the bioactive compounds in cells varied, including modulation of a cell cycle, activation of immune cells, damage of a lipid layer and mitochondrial membrane, activation of caspase proteins, inhibition of protein cell tumor invasion, metastasis, and angiogenesis, and also acts as an antioxidant. Therefore, the existence of the scientific studies results of this review with the potential availability of adequate rice bran in Indonesia is very potential to be developed.


Introduction
Bioactive compounds are phytochemicals that can be found in food, serves to modulate metabolic processes to improve health. The bioactive compounds in rice bran have been widely known that have a role in reducing several diseases such as hyperlipidemia (Um et al., 2013), antiproliferation in cancer cells (Hui et al., 2010;Zulfafamy et al., 2018;Islam et al., 2017;Ghoneum & Agrawal 2011), antidiabetic (Ardiansyah et al., 2006;Noviasari et al., 2019;Kurniawati et al., 2016), chronic kidney disease and acute coronary syndrome (Rashid et al., 2015).
Rice bran is a by-product of the rice milling process. In the process of rice milling, 10% of rice bran will be produced. The potential of rice bran that produced was estimated at 5.65 million tons in Indonesia in 2018 (Badan Pusat that act as antioxidant compounds are phenolic acids, anthocyanins, flavonoids, tocotrienols, tocopherols, γ-oryzanol, and phytic acid (Goufo et al., 2014). These groups are found in rice bran. The amount of bioactive compound and nutrient content in rice bran can be seen in Table 1.
Pigmented rice bran has been reported that is rich content in anthocyanin and proanthocyanidin. Both of them have a contribution to pigmented of rice, antioxidant (Limtrakul et al., 2019;Anggraini et al., 2015), anti-inflammatory (Limtrakul et al., 2016;Xia et al., 2006), and anthocyanin also act as cytotoxic activity (Pratiwi & Purwestri, 2017). Abdel-Aal et al., (2006) reported, the anthocyanin in black rice bran contained 3.276 mg/g and red rice bran contained 0.094 mg/g. While Hosoda et al., (2018) reported, that anthocyanin was only detected in black rice with the highest concentration, namely the Minenomurasaki cultivar (5.045,6 μg/g), while red rice was dominated by the proanthocyanidin component in the Yuyakemochi cultivar (3.060,6 μg/g). The variation in the amount of anthocyanin content is due to differences in rice cultivars and location of growth (Alauddina et al., 2017).
The compound of β-carotene and lycopene have been reported that it very contributes to the reddish-brown appearance, and both of them are precursors of vitamin A, which can act as antioxidants in the biological system (Lamberts et al., 2016). β-carotene and lycopene are part of the carotenoids. These carotenoids are able to bind singlet oxygen and to trap free peroxyl radicals, and it is called photoprotective agents (Manickavasagan et al., 2017). Brown rice bran was reported that contains dietary fiber which was four times higher than the white rice (Sun et al., 2010;Limtrakul et al., 2019), contained essential amino acids such as lysine (Limtrakul et al., 2019), and rich in content of vitamins, such as niacin (3.5-5.3), riboflavin (0.04-0.14), thiamine (0.29-0.61), and tocopherol (0.90 -2.50), units of measurement were shown here as mg/100 g of flour (Manickavasagan et al., 2017).
The bioactive component of γ-oryzanol which is present in rice bran (black, red, brown) was reported that had an antioxidant activity of 10 times higher than tocopherol, while oxaliplatin, and 5-fluorouracil (Nasrallah & Sibai, 2014).
Colon cancer itself was ranked the second highest cause of death in the world in 2018 (Bray et al., 2018). While in Indonesia, ranked the third highest (equivalent to the percentage of people with lung cancer), with the number of incidents in 2018 of 15.245 people, and will continue to increase until 2040 with an estimated number of 27.354 people, based on the 2018 Global Cancer Data (IARC, 2018). This disease is caused by two main factors, namely internal factors (5-10%) including genetic factors, and external factors (90-95%) such as stress, obesity, radiation, and bad dietary as the biggest contributing factor that is 30% to 35% (Anand et al., 2008). The effort of preventing cancer can be done, among others, by consuming functional food products. Rice bran which contents the bioactive compound can be used as ingredient for development of functional food products.
This article will review the potential of bioactive compounds in rice bran as the prevention of colon cancer. Scientific studies of bioactive compounds and their mechanisms for colon cancer will be reviewed in this article, which will be shown in the form of mapping. Furthermore, the development of rice bran as functional food will also be discussed to provide an illustration of the extent rice bran has been applied as a functional food.
Antioxidants have been reported that has a role in protecting cell damage due to oxidative stress resulting from the formation of free radicals, the oxidative stress is the main cause of cancer cases (Kumar, 2014). Groups  (Alauddina et al., 2017). These are detected much more in black rice bran. However, all rice bran types contain 4-hydroxy-3-methoxycinnamic acid, which is known to have antioxidative effects and photoprotective (Garcia-Conesa et al., 1999).

The Mechanism of Bioactive Compounds in Rice Bran as a Colon Cancer Prevention
The prevention mechanism of colon cancer cells by bioactive compounds in rice bran is reported very diverse, starting from acting as an antioxidant so that it can protect against free radicals, changing the cell cycle, cell antiproliferation, modulating the immune system, inducing apoptosis in the cascade pathway, and protecting the layers mucosa by influencing microbial transformation through high fiber content in rice bran (Henderson et al., 2012).
These mechanisms were also known different, both of the same or different groups of bioactive compounds, such as ferulic and p-coumaric acid, even though both were phenolic compound group, and capable to delay development in the Caco-2 colon cancer cell cycle, but through a different inhibitory pathway. Ferulic acid delayed on the S phase pathway, affected the centrosome central regulatory genes, and DNA damage checkpoint genes such as CEP2, CETN3, and RABGAP1. While p-coumaric acid induced the G2/M phase pathway and affected other cell cycle regulating genes, such as MYC, CDKN1A, PCNA, CDC25A, ODC1, CCNA2, and CCNB1 (Janicke et al., 2011).
Bioactive compound of p-coumaric acid not only played a role in delaying the cell cycle, but it was also reported to have the inhibitory ability on other mechanisms. Supplementation of p-coumaric acid on albino male rats, which was given procarcinogens 1,2 dimethylhydrazine (DMH) could inhibit glucose-regulated protein (GRP78) which was an indicator of transformation into malignant cancer, besides that, p-coumaric acid was able to mediate apoptosis against unfolded protein response (UPR) activated, which was the key to the development of oncogenic by inhibiting the expression of p-p65 (NF-κB) and p-IκBα, and reduced inflammation characterized by the decreased cytokine expression, namely COX-2, IL-6, TNF-α and PGE2 (Sharma et al., 2018).
UPR activation was reported to be able to activate anti-apoptotic NF-κB, thus inhibiting apoptotic signals from p53 and inducing angiogenic activity through increased vascular endothelial growth factor (VEGF) (Yadav et al., 2014). The increase of VEGF would cause cancer cells to receive nutrient and oxygen supply so that it was pushed to grow faster, inhibition of VEGF was also known to be regulated by COX-2, 5-LOX (Kim et al., 2012) and GRP78 enzymes through VEGFR-2 mediating signals (Katanasaka et al., 2010).
Another component that is also reported to play a role in inhibiting colon cancer is γ-oryzanol. Giving γ-oryzanol as feed to Balb/c mouse transplanted by colon cancer cells CT-26, was able to modulate the immune system by improving the function of phagocytosis in macrophages, released pro-inflammatory cytokines, tumor necrosis factor-α, IL-1β, and IL-6 by macrophages, increased the activity of natural killer cells (NK), reduced the number of blood vessels in cancer, suppressed vascular endothelial growth factor (VEGF) which was a marker of angiogenesis, and suppressed the COX-2 and 5-LOX enzymes (Kim et al., 2012). Phagocytosis is very important for cells to protect hosts against harmful foreign particles by swallowing and destroying them, and this process is very important as a form of immune response (Pavlou et al., 2017).
Other mechanisms of colon cancer cell inhibition are also reported, namely through the caspase cascade apoptosis pathway. This pathway can kill cancer cells without inflammation and damage to surrounding cells, by mediating by caspase which will produce an active signaling molecule, which acts as the main link in the regulatory network within the cell, so as to control cell death and inflammation (McIlwain et al., 2013). Apigenin (flavonoid group) was reported to be able to increase caspase-8 expression (initiator caspase), and caspase-3 (caspase executor) in HT-29 colon cancer cells, and could reduce cyclin D1 and rapamycin expression. Cyclin D1 acted as a protein that regulated cell cycles, while rapamycin was used as a clinical Table 2. Mechanism of inhibition of colon cancer cell proliferation by bioactive compounds in rice bran 289 pathological parameter in colorectal cancer patients (Turktekin et al., 2011).
The study of the potential of rice bran as an antiproliferation of colon cancer cells through the mechanism of biocative compounds, can be seen more comprehensively from the results of in vitro and in vivo studies presented in Table 2. In vivo study studies are presented to strengthen the evidence that the bioactive component present in bran, also works effectively in inhibiting colon cancer cells in experimental animal. The Development of Rice Bran as Functional Food The development of functional food from rice bran in Indonesia is still very limited. Even though data collection of BPS-Statistics Indonesia, Rice production in 2018 was 56.54 million tons, which meant the availability of rice bran potential could reach 5.65 million tons (Central Bureau of Statistics, 2018), that matter make of the processing of rice bran into functional food, that will have a high economic value. Furthermore, the potential of health is also very promising because the content of bioactive compounds is varied, such as high phenolic acids content in nonpigmented rice (1.96 mg GAE/g ), red rice bran (4.39 mg GAE/g), and black rice bran 6.65 (mg GAE/g), data were shown here as % dry weight (Moongngram et al., 2012), and also contain other bioactive compound such as γ-oryzanol, tocopherol, tocotrienol, anthocyanins, and flavonoids.
Some countries in the world such as the United States, Australia, and Japan have developed rice bran processed products to the commercial stage, such as rice bran cereal, rice bran dessert or energy drinks, rice bran tortillas, rice bran flakes, and rice bran oil. This situation is very different in Indonesia, which are generally still found are traditional foods, such as rice bran bangket, rice bran jenang or rice bran porridge (Widowati, 2001). Lack of public awareness about the benefits of rice bran, rice bran quality that has not been standardized, and the lack of downstream industries interested in developing rice bran, become obstacles in the effort to develop rice bran as a functional food (Tuarita et al., 2017).
There were some processed rice bran products that had actually been developed at a laboratory scale, such as tempe enriched by rice bran, so resulting in a total phenolic increased by 67% with a ratio of rice bran and soybean (4 :6) a . Chips products with the main ingredient of wheat flour mixed with bran-enriched soybean had increased protein content by 73% with a ratio of soybean flour and wheat flour (3: 7) b . Rice bran cereal (rice bran puffed cereal) with the application of twin screw extrusion technology, could produce a crisp texture and crisp resistance time in milk almost the same as or longer than commercial breakfast cereal products (Budijanto et al., 2012). Food bar from a mixture of rice bran flour and corn flour (10:90), was able to replace food bars made from wheat flour with insignificant differences in nutritional quality (protein, fat, carbohydrates), and qualify as emergency food with a total energy of 232.43 kcal/50 g of the ingredient (Kusumastuty et al., 2015). Furthermore, extrusion products from a mixture of rice and rice bran were reported to contain sufficient nutritional value and had the potential to be developed into snack products (Hermanianto et al., 2000).
The introduction of rice bran as a functional food is important to do. One way is by highlighting its health benefits as a marketing strategy. Thus, it is hoped to open the community paradigm and increase interest in the downstream industry as an effort to develop functional food from rice bran.

Conclusion
The bioactive compounds in rice bran consist of several categories, such as phenolic acids, flavonoids, anthocyanins, and steroidal compounds. The mechanisms of the bioactive compound rice bran in preventing colon cancer was classified by its function as an antioxidant, damage of the lipid layer and mitochondrial membrane, activation of immune cells, modulation of the cell cycle, inhibition of protein invasion of tumor cells, metastases, and angiogenesis, and activation of protein caspase to encourage apoptosis. The development of rice bran itself as a functional food product in Indonesia is still on a laboratory scale, although some are developed into traditional foods. Educating the public about the benefits of rice bran for health is a strategy for product development from rice bran raw material in the future.