Comparative antioxidant, antiproliferative and phase II enzyme inducing potential of sorghum (Sorghum bicolor) varieties

Epidemiological evidence has linked consumption of sorghum with reduced incidences of gastrointestinal cancer, especially cancer of esophagus. No information is available on how sorghum may effect the chemoprotective properties. We investigated in vitro potential of eight sorghum varieties to induce phase II detoxifying enzymes using the NAD(P)H:quinone oxidoreductase (NQO) enzyme assay, and also inhibit proliferation of esophageal, OE33, and colon, HT-29, carcinoma cells using the PicoGreen and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays; these properties were compared to phenolic profile and antioxidant activity of the sorghum. Black sorghum extract high in 3-deoxyanthocyanins was the most potent NQO inducer, doubling NQO activity at 5.0 mu g/mL and maximally inducing the enzyme activity by 3.0 times. White sorghum was a moderately strong inducer, maximally increasing NQO activity by 80%; tannin-containing sorghums were non-inducers. On the other hand, the tannin-containing sorghum extracts had strongest antiproliferative activity against both OE33 and HT-29 cells (IC50, 38-105 mu g/mL); the white sorghum extract was the least potent (IC50, 389 -> 800 mu g/mL). Antiproliferative activity correlated with antioxidant activity whereas NQO-inducer capacity did not. Sorghum extracts have strong chemoprotective potential which is partially independent of their antioxidant properties. They may thus be valuable health-promoting ingredients in whole-grain based products. (C) 2009 Elsevier Ltd. All rights reserved.