Efficiency of chelators in reversal of zinc-mediated cellular reactions incultured lung cells

Previous work using pulmonary cells in vitro indicated that inhibition of p rotein synthesis is an early and useful parameter in assessing zinc-mediate d cellular toxicity. We now have studied the restoration of protein synthes is with various zinc-chelating antidotes in cultured lung cell lines (A539, L2, 11Lu) after ZnCl2, treatment. After treatment with 75-200 mu M ZnCl2 f or 1-5 h to inhibit protein synthesis to 10-20% of control values, cells we re incubated in medium supplemented with either histidine [HIS], succinic a cid [SUCC], ethylenediaminetetraacetic acid [EDTA], 2,3-dimercaptopropane-1 -sulfonate [DMPS], d-penicillamine [dPA], or N-acetylcysteine [NAC], or eth ylenediamine [ED] in 10-fold molar excess over original zinc concentration. Alternatively, 2,3-dimercaptopropanol [BAL] was added at a concentration o f 400 mu mol/l (2-5.3-fold molar excess). Recovery of cellular function was assessed by measuring the increase of inhibited methionine incorporation. Antidote treatment elevated protein synthesis in the following order: DMPS greater than or equal to dPA > BAL greater than or equal to EDTA greater th an or equal to NAC greater than or equal to HIS > SUCC greater than or equa l to ED. Small differences were seen between the cell lines. HIS was effect ive in A549 cells only, whereas NAC did not recover protein synthesis in th ese cells. If antidote efficacy was ranked by reduced amounts of LDH leakag e, only DMPS and BAL were effective antidotes in 11Lu cells. In L2 and A549 cells no significant effects were seen using this parameter. Our results d o not agree well with in vivo data on zinc poisoning in mice (EDTA > dPA > DMPS); both series of antidote efficacy do not correlate with tabulated sta bility constants of binary complexes (dPA > EDTA > BAL > HIS > NAG). We con clude that orders of antidote efficiency obtained from in vivo systems migh t be extremely variable for each test system. Theoretically obtained data ( as complex building constants for chelating compounds as metal antidotes) d o nor necessarily consider pharmacokinetic properties. J. Trace Elem. Exp. Med. 13:215-226, 2000. (C) 2000 Wiley-Liss. Inc.