Increase of the Cellular Growth of Old Human Diploid Fibroblasts by Radical Scavenger: Water-Soluble Protein from Broad Beans

Abstract

There is increasing evidence that free radical scavengers play an important role in the aging process and the control of cellular growth. We purified a free radical scavenging protein, the water-soluble protein (WSP) from broad beans (Vicia faba). In this study, we examined the effect of WSP on cellular growth and in vitro life span in old human fetal lung fibroblasts (WI-38 and PDL 37-40, 78–84% of the maximum life span). Since WSP increased the cellular growth, we also examined the effect of WSP (1.25–5 µg/ml) on cytosolic antioxidant enzyme activities in the old cells treated or not with tert-butyl hydroperoxide (BHP) to elucidate the mechanisms of cell proliferation in the old cells. The cellular growth of old fibroblasts was greatly increased by WSP. In 1.25 and 2.5 µg/ml of WSP, the cell proliferation increased by 32 and 35%, respectively, as compared with controls. The maximum population doubling levels of the cells did not increase. In the cells incubated with BHP, the cytosolic superoxide dismutase activity was returned to its control value by WSP treatment (1.25–5 µg/ml). The cytosolic glutathione peroxidase activity progressively increased with increasing concentrations of WSP. On the other hand, the cytosolic superoxide dismutase activity after 1.25- and 2.5-µg/ml WSP treatment without BHP was increased by 189 and 144%, respectively. Similarly, the cytosolic glutathione peroxidase activity was increased by 67 and 53%, respectively. These results suggest that cytosolic antioxidant activities in old cells can be modulated by WSP treatment. We concluded that there was a correlation between the optimum WSP concentrations for the increase of cellular growth and the WSP concentrations required to exhibit these maximum enzyme activities.