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Abstract

The upcoming facts suggests that dietary rice bran has proved to exhibit some of the anticancer properties that inhibits the growth of cancer cells in areas such as breast, lung, liver, and colorectal. The bran portion of rice contains chemo-preventive ability such as ferulic acid, phytic acid, tricin, ?-sitosterol, ¥-oryzanol, and tocotrienols/tocopherols. The bioactive factors are initiated through their capacity to induce apoptosis, inhibit cell proliferation, and change the cell cycle growth in malignant cells. The bioactive portion of rice bran shields the damaging of tissue by scavenging the free radicals and restricting the chronic inflammatory responses. Also, the phytochemicals present in rice bran activates anticancer immune responses by affecting the colonic tumor micro environment by favoring the increase of colorectal cancer chemoprevention. This is obtained through the regulation of gut micro flora communities and the modulation of carcinogen-metabolizing enzymes.  Furthermore, the cost of rice production is considerably low and the availability of rice bran is easy, which makes it a winning performer in the global dietary chemoprevention. Hence, the function of dietary rice bran as a practical food-delivered chemo preventive means has the ability to have a notable effect on cancer prevention for the global population.

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Introduction

Despite the major developments in research, one of the main causes of mortality worldwide continues to remain cancer. According to the recent research conducted by the WHO, the burden of cancer remains to increase, with 70% of new cases registered in the developing world. Therefore, it’s important to spread the chemo preventive strategies with the development and implementation of novel, effective and affordable solutions that can reach the population across the globe.  In developed countries where there’s high-risk population, chemo preventive drugs such as non-steroidal anti-inflammatory drugs and tamoxifen, are being used. Although, due to risk of safety and high cost, these medicines are not very attractive to the developing countries. On the contrary, the consumption of whole foods which includes grains, vegetables, fruits, teas and spices has been associated with reduction in cancer risk, and their inherent safety makes these food items a rather better choice for long term use in diverse populations. In addition, the American Association for Cancer Research and  the World Cancer Research Fund have predicted that 30-40% of all types of cancers can  be prevented by the proper intake of dietary food and maintaining an appropriate body weight.

Epidemiological studies describes that the fiber from whole grains is helps significantly to lower the risk of colorectal cancer.  Over half of the world’s population consumes rice, oryza, sativa as its staple food. Most parts of the world, including the United States, consume white rice, although brown rice is a whole grain. Due to this, the chemo preventive research is mostly concentrated on brown rice and rice bran. The phytochemicals and nutrients present in rice bran have a vital rode in cancer-fighting and immune-enhancing.

Though there are various articles that give light on the chemo-preventive potential of the fiber and other whole grain, there has not been a comprehensive review targeting the chemo-preventive properties of rice bran. Hence, the major goal of this review is to highlight the effects and mechanisms of dietary rice bran for cancer chemoprevention.   

Rice bran and brown rice phytochemicals

There are a variety of bioactive components present in rice bran , having chemopreventive characteristics, which includes ¥-oryzanol , ferulic acid, caffeic acid, tricin, coumaric acid, phytic acid, the vitamib E isoforms ?-tacopherol, and various tocotrienols, phytosterols such a ?-sitosterol, stigmasterol, and capesterol; and carotenoids such as ?-carotene, ?-carotene, lutein, and lycopene. The other important components present in rice bran are cellulose, hemicelluslose, pectic, arabinoxylan, lignin, and ?-glucan; micronutrients such as calcium, magnesium, and 9B vitamins; tryptophan, histidine, cysteine, and arginine are the essential amino acids. Compared to other cereal brans, such as corn, wheat, and oat, the lipid fraction of rice bran contains a distinctive ratio of vitamin E isoforms ( ?-, ¥-, delta-tocotrienols and tocopherols ), ¥-oryzanol, and ?-sitosterol. It is discovered that the process of fermenting rice bran with bacterial or fungal agents can favourably alter the bioactivity. For instance, fermenting rice bran with Saccharomyces boulardii aided an increase in the quantity of ferulic acid released and decreased lymphoma cell viability unlike non-fermented rice bran. Various plant phenols, for example ferulic acid, are not frequently available for intake and fermentation of rice bran helps to improve the efficacy of the antioxidant activities. Fermented brown rice exhibits various properties like, cancer-fighting properties in vivo and research of the changes in bioactivity,metabolism, ananticancer activities after human consumption continued.     

 The figure represents a breakdown of the components found in dietary rice bran. Green boxes represent components with literature-supports cancer chemopreventive activity.

In Vitro Cancer Chemoprevention Study

The contribution of bioactive constituents like rice bran phytic acid,tricin, and flavonoids is focused on colorectal cancer chemoprevention. The growth of colorectal cancer cells is suppressed by the relative proportion of bioactive constituents in rice bran; although it varies among different varieties of rice. Kong et al says that the proliferation of human colorectal adenocarcinoma cell line is inhibited by rice bran phenolic compound cycloartenyl ferulate. Variety of cancer cell lines was studied for the cell-inhibiting activity in response to red rice bran extract and exhibited that red bran inherited strong inhibitory effects against leukemia, cervical, and stomach cancers. This was reported by Chen et al. In addition, Forster et al. also reported that rice bran, which consists of phenolica and ¥-tocotrienol , exhibited properties that notably decreased colorectal can cell proliferation ( p<0.05). On the other hand, another by-product of rice, namely momilactone B, which is an allelochemical of rice hull, has antiproliferative activity that protects the body against human leukeic T-cells through the activation of caspase and mitochondria pathways. Also, the growth of colon cancer cells is inhibited by methanol extract of rice husk, with the inhibition concentration (IC50) values of 0.5 µg/ml. Tan et al studied on the effect of brewers' rice on colorectal cancer cell line. Water extract of brewers' rice (WBR) restricted the proliferation of HT-29 cell line and the result was indicated to be associated with the bioactive compounds present in WBR although the extract was not a cytotoxic against normal cell lines. This information was consistent with the data received by Ryan et al., Fan et al., and Kong et al., who reported that the rice bran constituents were not cytotoxic against normal cell lines. In Vivo Cancer Chemopreventive Study It is found that rice germ or the components present in the rice bran or the germ have chemopreventive effects against carcinogenesis in the colon, liver, stomach, esophagus and bladder of rodents. Kong et al. found that rice bran cycloartenyl ferulate remarkably induced suppression of human colorectal adenocarcinoma of xenograft in nude mice after 21 days and triggered both death receptor and mitochondrial apoptosis pathways. Kim et al. observed the effect of rice bran ¥-oryzanol on colon tumor growth in pathogen-free female BALB/c mice. He discovered that rice bran ¥-oryzanol could restrict colon tumor and decreased the expression of vascular endothelial growth factor (VEGF) , Cyclooxygenase-2(COX-2), and 5-lipoxygenase (5-LOX). Choi et al, further explained that there was a reduction in VEGF,COX-2, and 5-LOX expression in mouse colon carcinoma cells-(CT-26-) treated mice by feeding a diet containing 10% (w/w) black and brown rice brans. An increase in COX-2 expression, which is an inflammatory gene, is related positively with the inflammatory response strength. Tan et al. researched that supplying AOM-induced colon cancer rats with a diet consisting 40% brewers' rice considerably reduced colon tumor multiplicity after 20 weeks of treatment (p<0.05). The greater concentration of brewers' rice bran treatment which has suppressive effects could be clearly understood by its higher concentrations of active compounds that may offer better functional properties. Nevertheless, it is not yet clear to the researchers about which bioactive constituents are in charge for the functional benefits of brewers' rice, however, it's possible to believe that several phytonutrients are responsible for these observed effects. Among the several studies conducted till date, the improvements of these indices could be credited to higher levels of ¥-oryzanol, phytic acid, vitamin E, and antioxidants. Hence, it is necessary to encourage long- term clinical studies to verify these results by obtaining different possible solutions and reduce the prevailing effect of cancer. Summary and Future Prospects  This review provides enough evidence both in vitro and in vivo that consumption of by-products of rice help the body to prevent cancer due to antioxidant phytonutrients present in them. The use of dietary bran proves to be a great future remedy for chemoprevention due to their unique bioactive compounds as per clinical studies. To conclude, the by-products of rice bran represents a distinctive approach to evaluate effective whole food compared to the individual phytochemical. The review gives a complete picture resulting from both in vitro and in vivo studies to gain a better realization of relationship between rice bran/ rice husk/ rice germ/ brewers' rice and cancers. The low cost and easy availability of rice by-products provides a better public health opportunity for people in developing and developed countries. Altogether, this research has paved way for a more likely use of rice         by-products in order to prevent and treat cancer. The potential use of the dietary by-products of rice replaces the conventional method of treatments and is guaranteed to be evaluated further in long-term clinical studies. 

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