Antimutagenic and Antioxidant Activities of Thai Rice Brans

BACKGROUND: Rice bran is the outer layer of the rice grain, and contains high amounts of bioactive phytochemicals. Here, we investigated and compared chemopreventive properties of purple and white rice bran extracts. METHODS: Rice bran was extracted with dichloromethane and methanol. Chemical constituents in the extracts were analyzed by colorimetric assay and high performance liquid chromatography. The mutagenicity and antimutagenicity of the extracts were determined via the Salmonella mutation assay. The anticarcinogenic enzyme induction and antioxidant activities of the extracts were examined using Hepa1c1c7 cells and 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, respectively. RESULTS: The methanol extracts of rice bran contained high amounts of phenolic acids, flavonoids, anthocyanins, and phytic acid, whereas large amounts of γ-oryzanol and vitamin E were presented in the dichloromethane extract. None of the extracts were mutagenic to Salmonella typhimurium. All rice bran extracts had strong antimutagenic effects against aflatoxin B1- and 2-amino-3,4-dimethylimidazo [4,5-f]quinoline-induced mutagenesis. The inhibitory effect against 2-aminofluorene-induced mutagenesis was found in the dichloromethane extract, while only the methanol extract of purple rice bran exhibited antimutagenic effects against benzo(a)pyrene. None of the extracts induced quinone reductase activity in Hepa1c1c7 cells. Additionally, the greatest antioxidant capacity was found in the methanol extract of purple rice bran. CONCLUSIONS: The methanol extract of purple rice bran containing high amount of phenolic acids, flavonoids, anthocyanins, and phytic acid showed the most effective antioxidant and antimutagenic activities by inhibiting mutagenic metabolizing enzymes and/or scavenging free radicals. These results demonstrate the nutritional and medical value of Thai rice for cancer prevention.

Toxicological and clastogenic evaluation of pinocembrin and pinostrobin isolated from Boesenbergia pandurata in Wistar rats

Pinocembrin (5, 7-dihydroxyflavanone) and pinostrobin (5-hydroxy-7-methoxy flavanone)are flavanones present in some natural products including the rhizome of Boesenbergia pandurata.Many reports showed their in vitro biological benefits without safety indication. The toxicity andmutagenicity of both flavanones in male Wistar rats were examined. There were no deaths observedfollowing a single oral administration of 500 mg/kg of both compounds. Body weight, vital organweights and blood biochemistry values of treated rats were not significantly different compared withthose of the control group. The mutagenicity of both flavanones using liver micronuclei in maleWistar rats was assessed. After feeding rats with 1-100 mg/kg for 7 days, the liver micronucleusformation and mitotic cells in hepatocytes were analyzed. Neither phytochemical affectedmicronucleus formation or mitotic index. Our results indicated that pinocembrin and pinostrobin arenon toxic and are not mutagenic to male Wistar rats within the 1-100 mg/kg interval.

Effect of Aqueous Extract from Cleistocalyx nervosum on Oxidative Status in Rat Liver

Cleistocalyx nervosum var. paniala, Ma-kiang, is a local plant in northern region of Thailand presenting high antioxidant activity in vitro. Our previous study found that 5 g/kg bw of C. nervosum aqueous extract had no acute toxic effect on rat. The present study was designed to determine effect of aqueous extract of C. nervosum on oxidative status in rat liver. Male Wistar rats were divided into 3 groups. Rats in group 1 were received water as a vehicle control, while group 2 and 3 were received 100 and 500 mg/kg bw of aqueous extract via intragastrium 5 times a week for 4 weeks. At the indicated time, the effect of C. nervosum on oxidative stress and antioxidant system were evaluated. Aqueous extract of C. nervosum did not affect the level of total glutathione, glutathione peroxidase and catalase activities. Low dose of C. nervosum (100 mg/kg bw) significantly increased malondialdehyde formation but high dose (500 mg/kg bw) did not. However, 500 mg/kg bw of C. nervosum extract significantly enhanced heme oxygenase-1 activity. Although the aqueous extract of C. nervosum at low dose exhibited the pro-oxidant effect but at high dose, it reduced oxidative stress in rat liver. In conclusion, the aqueous extract of C. nervosum might show biphasic effect on oxidative status of rat liver.