Visualization of labile zinc and its role in apoptosis of primary airway epithelial cells and cell lines

The respiratory epithelium is vulnerable to noxious substances, resulting i n the shedding of cells and decreased protection. Zinc (Zn), an antioxidant and cytoprotectant, can suppress apoptosis in a variety of cells. Here we used the novel Zn-specific fluorophore Zinquin to visualize and quantify la bile intracellular Zn in respiratory epithelial cells. Zinquin fluorescence in isolated ciliated tracheobronchial epithelial cells and intact epitheli um from sheep and pigs revealed an intense fluorescence in the apical and m itochondria-rich cytoplasm below the cilia. Zinquin fluorescence was quench ed by the Zn chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (T PEN) and increased by the Zn ionophore pyrithione. We also assessed whether changes in intracellular labile Zn would influence susceptibility of these cells to apoptosis by hydrogen peroxide. Our results confirm that Zn defic iency enhanced hydrogen peroxide-induced caspase activation from 1.24 +/- 0 .12 to 2.58 +/- 0.53 units.mug protein(-1).h(-1) (P less than or equal to 0 .05); Zn supplementation suppressed these effects. These findings are consi stent with the hypothesis that Zn protects upper respiratory epithelial cel ls and may have implications for human asthma where there is hypozincemia a nd epithelial damage.