Cytokinesis-block micronucleus cytome assays for the determination of genotoxicity and cytotoxicity of cecal water in rats and fecal water in humans

We tested the cytokinesis-block micronucleus cytome assay using the WIL2-NS human B lymphoblastoid cell line as a biomarker of genotoxicity and cytotoxicity of cecal water from rats and fecal water from humans. Cecal water was assessed in rats fed either a diet rich in fat, low in calcium and fiber, and barbecued red meat as the protein source (high colorectal cancer risk diet) or a diet high in fiber and calcium, low in fat, and casein as the protein source (low colorectal cancer risk diet) for 2 weeks. There was a significant 7.6-, 1.8-, and 4.0-fold increase in binucleated (BN) cells with micronuclei (Mn-BN), BN cells with nucleoplasmic bridges (Npb-BN), and necrotic cells (P < 0.001) with 1-h incubation with a 10% dilution of the cecal water isolated from rats fed the high colorectal cancer risk diet compared with rats fed the low colorectal cancer risk diet. In humans, fecal water samples collected from feces of free-living volunteers showed that 24-h exposure to 1% dilution of fecal water produced a significant 2.6-, 6.5-, 7.5-, and 2.2-fold increase in Mn-BN, Npb-BN, BN cells with nuclear buds, and necrotic cells compared with controls (P < 0.05). The coefficients of variations for interindividual differences for Mn-BN, Npb-BN, BN cells with nuclear buds, and necrosis biomarkers were greater than corresponding coefficients of variations for intraindividual variation. These results indicate that the cytokinesis-block micronucleus cytome assay can be used successfully to determine the interindividual variation in genotoxicity and cytotoxicity of cecal or fecal water and to identify dietary patterns that are likely to increase carcinogenic events in the colon.