FREE RADICAL-SCAVENGING PROPERTIES OF LIGNIN

Lignin is one of the major components of dietary fiber. It is a comple x hydrophobic molecule that typically occurs in cell walls with hetero xylans. Our experimental data show that lignin is a free radical scave nger. When the NADH-phenazine methosulfate-nitro blue tetrazolium free radical-producing system is used, an alkali-lignin concentration of 4 6.29 mu g/ml that causes 50% inhibition of uric acid production by xan thine oxidase (IC50) is a scavenger of superoxide anion radicals. Spec trophotometric assay has shown that alkali-lignin with an IC50 of 59.0 8 mu g/ml inhibits the activity of xanthine oxidase, one of the enzyme s related to the production of superoxide anion radicals, and presents a mixed-type noncompetitive inhibition pattern. Using the deoxyribose method, we have found that alkali-lignin is a hydroxyl radical scaven ger with an IC50 of 250 mu g/ml, and using the thiobarbituric acid met hod, we can see that alkali-lignin inhibits nonenzymatic and enzymatic lipid peroxidation with an IC50 of 72 and 100 mu g/ml, respectively. Alkali-lignin also hinders the activity of glucose-6-phosphate dehydro genase, another enzyme related to the generation of superoxide anion r adicals, with an IC50 of 123.6 mu g/ml, and obstructs the growth and v iability of cancer (HeLa) cells in a dose-dependent manner Our experim ental results suggest another mechanism whereby the free radical-scave nging activity of lignin in dietary fiber may be involved in the fiber -colon cancer interaction. We also suggest that the ability of dietary fiber to protect against colon cancer may be partly determined by the amount of lignin in dietary fiber as well as the free radical-scaveng ing ability of lignin.