Maha J Hashim and Jeffrey R Fry
Consumption of antioxidant compounds in the diet may provide cytoprotection against oxidative damage associated with diseases or exposure to toxic agents. In the present study, we have investigated the influence of extracellular protein-binding on the cytoprotective properties of two free-radical-scavenging natural products: quercetin (Q) and epigallocatechin-3-gallate (EGCG). Cytoprotection was determined by the ability of Q/EGCG to reduce the toxicity elicited by the oxidant tert-butyl hydroperoxide (t-BHP) in human hepatoma HepG2 cells, performed in serum-free medium or medium containing low [2%(v/v)] or high [10%(v/v)] levels of foetal bovine serum. Initial studies confirmed that the presence of serum (up to 10% v/v) was without effect on HepG2 viability. Furthermore, Q and EGCG were not toxic (up to a concentration of 100 μg/mL) under any of the culture conditions. Cytoprotection elicited by Q was significantly greater in serum-free and low-serum conditions compared to high-serum conditions. Similar results were obtained with EGCG, with additional evidence of a significant difference between serum-free and low-serum conditions. In conclusion, cytoprotective effects of Q and EGCG are modified by the presence of extracellular protein.
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