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

Abstract

Previous work using pulmonary cells in vitro indicated that inhibition of protein synthesis is an early and useful parameter in assessing zinc-mediated cellular toxicity. We now have studied the restoration of protein synthesis with various zinc-chelating antidotes in cultured lung cell lines (A549, L2, 11Lu) after ZnCl2 treatment. After treatment with 75–200 μM ZnCl2 for 1–5 h to inhibit protein synthesis to 10–20% of control values, cells were incubated in medium supplemented with either histidine [HIS], succinic acid [SUCC], ethylenediaminetetraacetic acid [EDTA], 2,3-dimercaptopropane-1-sulfonate [DMPS], d-penicillamine [dPA], or N-acetylcysteine [NAC], or ethylenediamine [ED] in 10-fold molar excess over original zinc concentration. Alternatively, 2,3-dimercaptopropanol [BAL] was added at a concentration of 400 μmol/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 ≥ dPA > BAL ≥ EDTA ≥ NAC ≥ HIS > SUCC ≥ ED. Small differences were seen between the cell lines. HIS was effective in A549 cells only, whereas NAC did not recover protein synthesis in these cells. If antidote efficacy was ranked by reduced amounts of LDH leakage, 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 do 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 stability constants of binary complexes (dPA > EDTA > BAL > HIS > NAC). We conclude that orders of antidote efficiency obtained from in vivo systems might be extremely variable for each test system. Theoretically obtained data (as complex building constants for chelating compounds as metal antidotes) do not necessarily consider pharmacokinetic properties. J. Trace Elem. Exp. Med. 13:215–226, 2000. © 2000 Wiley-Liss, Inc.