Abstract
BackgroundRice 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.MethodsThis 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.ResultsThe 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.ConclusionsPRHE 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.
Highlights
Rice husk, a waste material produced during milling, contains numerous phytochemicals that may be sources of cancer chemopreventive agents
white rice husk extract (WRHE) slightly reduced the number of micronucleated hepatocytes induced by Aflatoxin B1 (AFB1) but showed no significant difference when compared with the AFB1 treated group. These results suggested that purple rice husk extract (PRHE) was more efficient than WRHE in inhibiting genotoxicity induced by AFB1
We found that the patterns of several phase I and II metabolizing enzyme activities differed from those observed in other studies of AFB1 metabolism [32, 33]
Summary
A waste material produced during milling, contains numerous phytochemicals that may be sources of cancer chemopreventive agents. There are few comparative studies of the cancer chemopreventive effects of white and colored rice husk. AFB1 is the most potent hepatocarcinogen in humans and animals; the toxin is capable of inducing mutations in specific vital genes in hepatocytes, leading to cancer initiation [1]. The rat liver micronucleus assay is considered as a reliable test for genotoxicants, since the liver is a major source of XMEs [4]. Both bacterial mutation assays and micronucleus tests have been modified for assessing antigenotoxicity of natural products
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