On the toxic effects of tetraethyl lead and its derivatives on the chrysophyte Poterioochromonas malhamensis. VII. Protective action of thiol compounds, vitamins, trace elements, and other agents.

The influence of 45 different substances on the growth inhibiting effects of triethyl lead chloride (TriEL) in cultures of the unicellular alga Poterioochromonas malhamensis was studied. Ten thiol or disulfide compounds, 9 vitamins, 12 trace elements, 14 miscellaneous agents, and 9 combinations of these agents were tested. The agents were applied to the algal cultures in three different concentrations simultaneously with 10 microM TriEL and incubated for 72 hr. While none of the tested thiol and disulfide compounds remarkably protected the algae from TriEL toxicity, two vitamins (tocopheryl acetate, ascorbic acid), one trace element (zinc), adenosine-5'-triphosphate Na2 salt, cyclic AMP, and concanavalin A as well as combinations of some of these agents were found to suppress markedly the growth inhibiting effects of TriEL. Zinc was the most effective agent; it increased algal growth in TriEL-treated cultures by about 70 times as compared with cultures containing TriEL alone. A combination of 10 essential trace elements was even more protective and almost completely suppressed TriEL toxicity. In contrast to this, some of the other agents potentiated the toxic effects of TriEL (e.g., magnesium, molybdenum, caffeine, deuteriumoxide, chlorpromazine, dimethylsulfoxide) in the tested concentration ranges. The most protective agents Zn, VitC, and VitE did not prevent the inhibitory effects of TriEL on microtubule (MT) assembly in vitro, suggesting that their in vivo protection is based on mechanisms other than direct protecting MTs from the attack of the lead compound. Zn had no direct influence on the stability and half life of TriEL in the growth medium. The lack of protection found by the thiol compounds used suggests that most probably general thiol interaction of TriEL is not its major toxic mechanism of action. It is postulated that the protective action of Zn, VitE, and VitC is directly or indirectly mediated by suppression of TriEL-induced peroxidation processes in the poisoned algae. The protective agents found provide a basis for further screening experiments in order to test their "therapeutic" potency in experimental animals poisoned with organolead.