Antimutagenic and Antioxidant Activities of Thai Rice Brans

Cancer chemopreventive potential of cooked glutinous purple rice on the early stages of hepatocarcinogenesis in rats

Cancer prevention using dietary phytochemicals holds great potential, particularly in the alternative treatment of liver cancer. Our previous study found that the methanol extract of cooked purple rice performed various biological functions including antioxidant, anti-inflammatory, and antimutagenic activities in in vitro assays. This study aimed to evaluate the chemopreventive effects of cooked glutinous purple rice extract (CRE) obtained from routine rice cooking method on diethylnitrosamine (DEN)-induced hepatic preneoplastic lesions in rats, along with its inhibitory mechanisms. CRE containing γ-oryzanols and high amounts of polyphenolic compounds, particularly cyanidin-3-glucoside, was fed to rats over a period 15 weeks. Additionally, injections of triple DEN at a concentration of 100 mg/kg BW were administered to rats once a week during the second, third, and fourth weeks of the experiment. The results revealed that CRE did not induce the formation of glutathione S-transferase placental form (GST-P) positive foci as a precancerous lesion during rat hepatocarcinogenesis, indicating non-carcinogenicity. Furthermore, CRE significantly reduced the number and size of GST-P positive foci in DEN-initiated rats. It also modulated microenvironment homeostasis by reducing the number of PCNA positive hepatocytes and by enhancing the number of apoptotic positive hepatocytes in the livers of DEN-initiated rats. Using RT-PCR analysis, CRE decreased the mRNA expression of some proinflammatory mediators, including interleukin-6, interleukin-1 beta, inducible nitric oxide synthase and cyclooxygenase 2, by attenuating the expression of cyclin E, the proliferation marker, while also inducing the expression of the apoptotic gene, Bcl2 associated X. The inhibitory mechanism at the early stages of hepatocarcinogenesis of CRE may be involved with the attenuation of cell proliferation, the enhancement of apoptosis, and the modulation of the proinflammatory system. Anthocyanins, flavonoids, and γ-oryzanol represent a group of promising chemopreventive agents in cooked glutinous purple rice extract. The outcomes of this study can provide an improved understanding of the potential role of the phytochemicals contained in cooked purple glutinous rice with regard to cancer alleviation.

Comparative RNA-Seq analysis unravels molecular mechanisms regulating therapeutic properties in the grains of traditional rice Kavuni

Developing rice varieties with enhanced levels of functional bioactives is an important intervention for achieving food and nutritional security in Asia where rice is the staple food and Type II diabetes incidences are higher. The present study was aimed at dissecting out the molecular events underlying the accumulation of bio active compounds in pigmented traditional rice Kavuni. Comparative transcriptome profiling in the developing grains of Kavuni and a white rice variety ASD 16 generated 37.7 and 29.8 million reads respectively. Statistical analysis identified a total of 9177 exhibiting significant differential expression (DEGs) between the grains of Kavuni and ASD 16. Pathway mapping of DEGs revealed the preferential up-regulation of genes involved in the biosynthesis of amylose and dietary fibres in Kavuni accounting for its low glycemic index (GI). Transcripts involved in the biosynthesis of carotenoids, flavonoids, anthocyanins, phenolic acids and phenylpropanoids were also found to be up-regulated in the grains of Kavuni. This study identified up-regulation of key transcripts involved in the accumulation of phenolic acids having potential for inhibiting major hydrolytic enzymes α-amylase and α-glucosidase and thus accounting for the slow digestibility leading to low GI. Overall, this study has identified molecular targets for the genetic manipulation of anti-diabetic and anti-oxidant traits in rice.

Phytochemical Profile and Chemopreventive Properties of Cooked Glutinous Purple Rice Extracts Using Cell-Based Assays and Rat Model

Purple rice has gained attention for its health promoting potential due to a high content of bioactive phytochemicals. The heat generated during cooking alters the quality and quantity of nutrients and phytochemicals in food. This study aimed to investigate the phytochemical profile and chemopreventive properties of cooked glutinous purple rice using cell-based assays and a rat model. Purple rice was cooked in a rice cooker and was then further extracted with solvents to obtain dichloromethane and methanol extracts. The methanol extracts of glutinous purple rice contained great amounts of phenolics, flavonoids, and anthocyanins. Protocatechuic acid (2.26–5.40 mg/g extract) and cyanidin 3-glucoside (34.3–65.7 mg/g extract) were the major phenolic acid and anthocyanin contents, respectively. After cooking, the content of anthocyanins, γ-oryzanols, and phytosterols decreased, while the amount of some phenolic acid and tocol contents increased. Methanol extracts of glutinous purple rice inhibited reactive oxygen species production about 60% in PMA-treated peripheral blood mononuclear cells, reduced nitric oxide formation in LPS-induced RAW 264.7 cells (26–39% inhibition), and exhibited antimutagenicity against several mutagens using the Ames test, but dichloromethane extracts presented only mild anti-inflammatory activities. Although methanol extracts induced mild mutagenicity (mutagenic index 2.0–2.5), they did not induce micronucleated hepatocyte formation and certain hepatic CYP450 isozyme activities in rats. However, the mutagenicity of the methanol extract significantly declined after cooking. In summary, the methanol extract of the cooked glutinous purple rice might be a promising cancer chemopreventive fraction, which was neither genotoxic nor posing adverse effects on phytochemical–drug interaction in rats.

Rice varieties with a high endosperm lipid content have reduced starch digestibility and increased γ-oryzanol bioaccessibility

The amount and distribution of rice endosperm lipids can influence starch digestibility and nutritional properties of white rice. However, this aspect has been poorly investigated thus far. We investigated the digestion properties of five rice varieties and common rice having different lipid contents (8.1-24.2 g kg^-1) showing that the lipid content is positively correlated with the resistant starch content and negatively correlated with digestion extent (C_∞) and estimated glycemic index (eGI). After non-starch lipid (NSL) removal from selected high-lipid mutants (ALK3 and RS4), C_∞ was significantly enhanced compared to native samples when digested by α-amylase, while this phenomenon was not observed in low-lipid rice (GZ93). When pancreatin was used, starch digestion was only delayed; triglycerides were gradually hydrolyzed by pancreatic lipase and the lipids-starch complex became no longer resistant to hydrolysis by α-amylase. These results indicated that rice endosperm lipids inhibited starch digestion, by transforming part of the starch into a slowly digestible starch fraction. High-lipid mutants also had a higher total amount of, and more bioaccessible, γ-oryzanol than low-lipid varieties. This study indicates that high-lipid white rice has great potential in designing functional rice-based foods, combining a relatively lower eGI and a high γ-oryzanol content.

Mutagenic potential of medicinal plants evaluated by the Ames Salmonella/microsome assay: A systematic review

The Ames test has become one of the most commonly used tests to assess the mutagenic potential of medicinal plants since they have several biological activities and thus have been used in traditional medicine and in the pharmaceutical industry as a source of raw materials. Accordingly, this review aims to report previous use of the Ames test to evaluate the mutagenic potential of medicinal plants. A database was constructed by curating literature identified by a search on the electronic databases Medline (via Pubmed), Science Direct, Scopus, and Web of Science from 1975 to April 2020, using the following terms: "genotoxicity tests" OR "mutagenicity tests" OR "Ames test" AND "medicinal plants." From the research, 239 articles were selected, including studies of 478 species distributed across 111 botanical families, with Fabaceae, Asteraceae and Lamiaceae being the most frequent. It was identified that 388 species were non-mutagenic. Of these, 21% (83/388) showed antimutagenic potential, most notable in the Lamiaceae family. The results also indicate that 18% (90/478) of the species were mutagenic, of which 54% were mutagenic in the presence and absence of S9. Strains TA98 and TA100 showed a sensitivity of 93% in detecting plant extracts with mutagenic potential. However, the reliability of many reviewed studies regarding the botanical extracts may be questioned due to technical issues, such as testing being performed only in the presence or absence of S9, use of maximum doses below 5 mg/plate and lack of information on the cytotoxicity of tested doses. These methodological aspects additionally demonstrated that a discussion about the doses used in research on mixtures, such as the ones assessed with botanical extracts and the most sensitive strains employed to detect the mutagenic potential, should be included in a possible update of the guidelines designed by the regulatory agencies.

The Genetic Basis and Nutritional Benefits of Pigmented Rice Grain

Improving the nutritional quality of rice grains through modulation of bioactive compounds and micronutrients represents an efficient means of addressing nutritional security in societies which depend heavily on rice as a staple food. White rice makes a major contribution to the calorific intake of Asian and African populations, but its nutritional quality is poor compared to that of pigmented (black, purple, red orange, or brown) variants. The compounds responsible for these color variations are the flavonoids anthocyanin and proanthocyanidin, which are known to have nutritional value. The rapid progress made in the technologies underlying genome sequencing, the analysis of gene expression and the acquisition of global 'omics data, genetics of grain pigmentation has created novel opportunities for applying molecular breeding to improve the nutritional value and productivity of pigmented rice. This review provides an update on the nutritional value and health benefits of pigmented rice grain, taking advantage of both indigenous and modern knowledge, while also describing the current approaches taken to deciphering the genetic basis of pigmentation.

Inhibitory effect of purple rice husk extract on AFB1-induced micronucleus formation in rat liver through modulation of xenobiotic metabolizing enzymes

Background

Rice husk, a waste material produced during milling, contains numerous phytochemicals that may be sources of cancer chemopreventive agents. Various biological activities of white and colored rice husk have been reported. However, there are few comparative studies of the cancer chemopreventive effects of white and colored rice husk.

Methods

This study investigated the cancer chemopreventive activities of two different colors of rice husk using in vitro and in vivo models. A bacterial mutation assay using Salmonella typhimurium strains TA98 and TA100 was performed; enzyme induction activity in murine hepatoma cells was measured, and a liver micronucleus test was performed in male Wistar rats.

Results

The white rice husk (WRHE) and purple rice husk (PRHE) extracts were not mutagenic in Salmonella typhimurium TA98 or TA100 in the presence or absence of metabolic activation. However, the extracts exhibited antimutagenicity against aflatoxin B₁ (AFB₁) and 2-amino-3,4 dimethylimidazo[4,5-f]quinolone (MeIQ) in a Salmonella mutation assay. The extracts also induced anticarcinogenic enzyme activity in a murine Hepa1c1c7 hepatoma cell line. Interestingly, PRHE but not WRHE exhibited antigenotoxicity in the rat liver micronucleus test. PRHE significantly decreased the number of micronucleated hepatocytes in AFB₁-initiated rats. PRHE contained higher amounts of phenolic compounds and vitamin E than WRHE in both tocopherols and tocotrienols as well as polyphenol such as cyanidin-3-glucoside, protocatechuic acid and vanillic acid. Furthermore, PRHE increased CYP1A1 and 1A2 activities while decreasing CYP3A2 activity in the livers of AFB₁-treated rats. PRHE also enhanced various detoxifying enzyme activities, including glutathione S-transferase, NAD(P)H quinone oxidoreductase and heme oxygenase.

Conclusions

PRHE showed potent cancer chemopreventive activity in a rat liver micronucleus assay through modulation of phase I and II xenobiotic metabolizing enzymes involved in AFB₁ metabolism. Vitamin E and phenolic compounds may be candidate antimutagens in purple rice husk.

Electronic supplementary material

The online version of this article (10.1186/s12906-019-2647-9) contains supplementary material, which is available to authorized users.

Protective Effects of Defatted Sticky Rice Bran Extracts on the Early Stages of Hepatocarcinogenesis in Rats

Use of natural products is one strategy to lessen cancer incidence. Rice bran, especially from colored rice, contains high antioxidant activity. Cancer chemopreventive effects of hydrophilic purple rice bran extract (PRBE) and white rice bran extract (WRBE) on carcinogen-induced preneoplastic lesion formation in livers of rats were investigated. A 15-week administration of PRBE and WRBE did not induce hepatic glutathione S-transferase placental form (GST-P) positive foci formation as the biomarker of rat hepatocarcinogenesis. PRBE and WRBE at 500 mg/kg body weight significantly decreased number and size of GST-P positive foci in diethylnitrosamine (DEN)-initiated rats. The number of proliferating nuclear antigen positive hepatocytes were also reduced in preneoplastic lesions in both PRBE and WRBE fed DEN-treated rats. Notably, the inhibitory effect on GST-P positive foci formation induced by DEN during the initiation stage was found only in rats treated by PRBE for five weeks. Furthermore, PRBE attenuated the expression of proinflammatory cytokines involving genes including TNF-α, iNOS, and NF-κB. PBRE contained a higher number of anthocyanins and other phenolic compounds and vitamin E. PRBE might protect DEN-induced hepatocarcinogenesis in rats via attenuation of cellular inflammation and cell proliferation. Anthocyanins and other phenolic compounds, as well as vitamin E, might play a role in cancer chemopreventive activity in rice bran extract.

Modulation of plasma and urine metabolome in colorectal cancer survivors consuming rice bran

Rice bran has bioactive phytochemicals with cancer protective actions that involve metabolism by the host and the gut microbiome. Globally, colorectal cancer (CRC) is the third leading cause of cancer-related death and the increased incidence is largely attributed to poor dietary patterns, including low daily fiber intake. A dietary intervention trial was performed to investigate the impact of rice bran consumption on the plasma and urine metabolome of CRC survivors. Nineteen CRC survivors participated in a randomized-controlled trial that included consumption of heat-stabilized rice bran (30 g/day) or a control diet without rice bran for 4 weeks. A fasting plasma and first void of the morning urine sample were analyzed by non-targeted metabolomics using ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). After 4 weeks of either rice bran or control diets, 12 plasma and 16 urine metabolites were significantly different between the groups (p≤0.05). Rice bran intake increased relative abundance of plasma mannose (1.373-fold) and beta-citrylglutamate (BCG) (1.593-fold), as well as increased urine N-formylphenylalanine (2.191-fold) and dehydroisoandrosterone sulfate (DHEA-S) (4.488-fold). Diet affected metabolites, such as benzoate, mannose, eicosapentaenoate (20:5n3) (EPA), and N-formylphenylalanine have been previously reported for cancer protection and were identified from the rice bran food metabolome. Nutritional metabolome changes following increased consumption of whole grains such as rice bran warrants continued investigation for colon cancer control and prevention attributes as dietary biomarkers for positive effects are needed to reduce high risk for colorectal cancer recurrence.

Nutritional composition of Eragrostis teff and its association with the observed antimutagenic effects

Eragrostis teff is an Ethiopian native grass plant (Poaceae or Gramineae family) whose importance as a crop grain has increased in recent years. The aim of this study is to analyze the nutritional composition of its seeds and the mutagenic/antimutagenic activity of the hydroalcoholic extract of the seed flour. Chemical elements (colloquially known as minerals) were determined using Particle-Induced X-ray Emission (PIXE) and Flame Atomic Absorption Spectroscopy (FAAS), while the content of amino acids (aminogram) and fatty acids (profile of fatty acids) were quantified by HPLC. Mutagenic activities were tested using Salmonella/microsome assay. Mutagens doxorubicin, 4-nitroquinolin N-oxide, methylmethanosulphonate, and aflatoxin B-1 were used in Salmonella typhimurium TA98 and TA100 strains to assess antimutagenic activities. The major elements observed were K, P, S, Mg, and Ca. Almost all essential amino acids were observed and the predominance of unsaturated fatty acids in the total oil content of 2.72% (w/w) is also noted, including the two essential fatty acids alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). Hydroalcoholic extract of E. teff seed flour showed antimutagenic activity, protecting against frameshift and base pair substitution mutations. These findings provide valuable information for further development of healthier foods that can be produced with increasing yields and minimal environmental impact.

Eragrostis teff is an Ethiopian native grass plant (Poaceae or Gramineae family) whose importance as a crop grain has increased in recent years.