In vitro cytotoxic effects of enzymatically induced oxygen radicals in human fibroblasts: Experimental procedures and protection by radical scavengers.

Introduction of hypoxanthine and xanthine oxidase into human fibroblast cultures induces a dose-dependent cytotoxicity as a result of free-radical formation. The influence of medium, cell density and the power of recovery after free-radical attack were investigated. It appears that toxicity is higher in physiological Dulbecco phosphate buffer or Hanks' balanced salt solution than in modified Eagle medium, is inversely proportional to cell density and that damage is most often irreversible. Using this model, we studied the protective effects of a hydrosoluble flavonoid, silybin, and of a well known antioxidant, BHT (butylated hydroxytoluene). These molecules were administered before and during free-radical attack. With BHT significant protection was observed when it was added before free-radical attack (24% protection at a concentration of 10(-4)m) and before and during exposure (20% protection at a concentration of 10(-5)m). When silybin is applied during radical attack maximal activity is recorded at a concentration of 8 x 10(-4)m (45%), but the most interesting results are observed when 1 x 10(-4) and 8 x 10(-4)m are used, respectively, before and during radical exposure (63% of activity).