PROTECTION BY THE HEAVY-METAL CHELATOR N,N,N',N'-TETRAKIS (2-PYRIDYLMETHYL)ETHYLENEDIAMINE (TPEN) AGAINST THE LETHAL ACTION OF BOTULINUM NEUROTOXIN-A AND NEUROTOXIN-B

The ability of N,N,N',N'-tetrakis (2-pyridylmethyl)-ethyenediamine (TP EN) to protect against botulinum neurotoxin (BoNT) A and B was examine d in vivo in mice. To determine the protective effcacy of TPEN, mice w ere injected i.p. with TPEN as a single bolus or as multiple injection s 30 min before and 0, 2, 4 and 6 hr following i.v. challenges with Bo NT-A or -B. TPEN treatment did not alter the 24 hr lethality of BoNT b ut did produce a significant delay in the time to death. For a moderat e dose of serotype A (20 LD50), five divided doses of TPEN prolonged t he time to death from 7.8 +/- 0.4 hr to 9.9 +/- 0.5 hr. For serotype B , examined under comparable conditions, the prolongation of the time t o death was from 6.1 +/- 0.2 hr to 9.4 +/- 0.6 hr. The range of TPEN d oses that could be examined in vivo was limited by its acute toxicity, Although low doses of TPEN (less than or equal to 10 mg/kg) were well tolerated, higher doses (greater than or equal to 30 mg/kg) led to at axia, loss of coordination, convulsions and death in 20.3 min or less. In clonal NG108-15 cells, TPEN was found to produce cytotoxicity as r evealed by increases in the secretion of the marker enzyme lactate deh ydrogenase (LDH), and enhanced reactivity with the vital dye trypan bl ue. From LDH concentration-response data determined 24 hr after additi on of TPEN, the threshold concentration for observing cytotoxicity was 10 mu M and the IC50 was 19.8 mu M. At the highest TPEN concentration tested (100 mu M), cytotoxicity was detected 8 hr after TPEN addition and increased in severity over a 3 day period. The cytotoxicity in NG 108-15 cells appears to be distinct from the rapid-onset toxicity obse rved in whole animals. These results suggest that TPEN may be of poten tial benefit in delaying the lethal actions of BoNT-A and -B, but its use is limited by its initial and delayed toxicity. Since the therapeu tic and toxic actions of TPEN are both related to zinc chelation, the use of TPEN would need to be restricted to low doses as part of a comb ination therapy. Published by Elsevier Science Ltd.