Zinc deficiency induces oxidative stress and AP-1 activation in 3T3 cells

It has been postulated that one mechanism underlying zinc deficiency-induced tissue alterations is excessive cellular oxidative damage. In the present study we investigated if zinc deficiency can induce oxidative stress in 3T3 cells and trigger select intracellular responses that have been associated to oxidative stress. Cells were exposed to control media or to chelated media containing 0.5, 5, or 50 microM zinc for 24 or 48 h. The oxidative status of the cells was evaluated as an increase in the fluorescence of the probe 5(or 6)-carboxy-2'7'-dichlorodihydrofluorescein diacetate (DCDCDHF). After 24 and 48 h of exposure, the fluorescence intensity was significantly higher (4- to 15-fold) in the 0.5 and 5 microM Zn groups compared to the 50 microM Zn and control groups. The activity of the antioxidant enzymes CuZn (CuZnSOD) and Mn (MnSOD) superoxide dismutases was significantly higher in the 0.5 and 5 microM Zn cells compared to the 50 microM Zn and control groups at both the 24 and 48 h time points. These higher activities were associated with higher levels of MnSOD mRNA. After 24 h in culture, the level of activated AP-1 was markedly higher in the 0.5 and 5 microM Zn cells than in the control (72 and 58%, respectively) and 50 microM Zn cells (73 and 60%, respectively). NF-kappaB binding activity was lower in the 0.5 and 5 microM Zn cells than in controls. Thus, oxidative stress is induced by zinc deficiency in 3T3 cells. This oxidative stress results in an upregulation of oxidant defense mechanisms.