Although epidemiologic evidence supports an inverse association between whole grain consumption and cancer risk, results are inconclusive as to the precise bioactive food components by which chemoprevention occurs. Emerging data has identified phytochemicals contained in rice bran that may reduce cancer risk;however, little is known about the concentrations and bioavailability of these chemopreventive phytochemicals in existing varieties and landraces of cultivated rice. Rice (Oryza sativa) is the primary source of dietary calories for half of humanity and is the first crop plant for which a high-quality reference genome sequence has been produced. Rice varieties that capture the impressive genotypic and phenotypic diversity of domesticated rice world-wide should be investigated for differential cancer prevention properties. Moreover, an extensive review of the literature revealed limited research aimed at exploring the role probiotics play in metabolizing rice bran. Thus, the development of an experimental model to assess the effects of rice bran-probiotic interactions on bioavailability of chemopreventive compounds to blood, lymphocytes and lymph nodes is proposed. Findings from the studies proposed herein will fill a significant gap in our knowledge regarding rice bran phytochemical diversity and bioavailability for chemoprevention. The stoichiometry of selected bioactive rice bran components with reported cancer prevention properties will be determined in three genetically diverse rice cultivars. These rice varieties will be fermented with probiotics, Lactobacillus caseii and Bifidobacteria longum, and one resident non-probiotic, Escherichia coli, in Aim 1 to determine their effect on levels of the selected metabolites. The probiotic digestion of rice bran is hypothesized to enhance bioavailability of rice bran derived chemopreventive compounds. Phytochemicals and metabolites will be detected by liquid and gas chromatography coupled with -mass spectrometry (LC-MS, GC-MS).
A second aim i s proposed to determine the dose of rice bran that achieves greatest bioavailability of target phytochemicals and metabolites into blood, lymphocytes and lymph nodes of naturally occurring canine lymphoma patients. This comparative oncology model is novel for assessing bioavailability of dietary rice bran components. Furthermore, it has been well established that naturally developing canine cancer exhibits greater translational potential compared to experimentally induced cancer in rodents, particularly for lymphoma. The pilot dose determination studies are feasible for testing the hypothesis that bioavailability of cancer prevention compounds from dietary whole rice bran intake varies across genetically diverse rice cultivars and by probiotic fermentation. Indeed, pre-clinical and clinical studies that evaluate the role of fiber or isolated rice bran compounds and cancer risk are conflicting, and we put forth that novel transdisciplinary scientific approaches are necessary to advance the nutritional investigation of rice bran for cancer prevention.
Stabilized rice bran is a unique whole food that naturally contains protein, vitamins, minerals, complex carbohydrates, phytonutrients, phospholipids, essential fatty acids, and more than 120 antioxidants. Rice bran phytochemicals have demonstrated cancer prevention activity, however not all rice varieties are equal in content and composition. The diversity of rice bran components across unique rice varieties and the probiotic metabolism of select phytochemicals are important considerations that merit further investigation when assessing bioavailability of rice bran components for chemoprevention.
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