The adverse events caused by botulinum toxin type A (subtype A1) product, thought to be after-effects of toxin diffusion after high-dose administration, have become serious issues. A preparation showing less diffusion in the body than existing drugs has been sought. We have attempted to produce neurotoxin derived from subtype A2 (A2NTX) with an amino acid sequence different from that of neurotoxin derived from subtype A1 (A1NTX). In this study, to investigate whether A2NTX has the potential to resolve these issues, we compared the safety of A2NTX, a progenitor toxin derived from subtype A1 (A1 progenitor toxin) and A1NTX employing the intramuscular lethal dose 50% (im LD 50 ) in mice and rats and the compound muscle action potential (CMAP) in rats. Mouse im LD 50 values for A1 progenitor toxin and A2NTX were 93 and 166 U/kg, respectively, and the rat im LD 50 values were 117 and 153 U/kg, respectively. In the rat CMAP test, the dose on the contralateral side, which caused a 50% reduction in the CMAP amplitude, that is, CMAP-TD 50 , was calculated as 19.0, 16.6 and 28.7 U/kg for A1 progenitor toxin, A1NTX and A2NTX, respectively. The results indicate that A2NTX is safer than A1 progenitor toxin and A1NTX.Botulinum toxins act on neuromuscular junctions and inhibit the release of acetylcholine from pre-junctional membranes, inducing muscle relaxation [1][2][3][4]. The toxins have been used as important therapeutic agents for neurological disorders [5][6][7]. There are seven subtypes of type A organism, A1-A7, based on variations in the amino acid sequence of the neurotoxin produced [8][9][10], and all botulinum toxin type A products are derived from subtype A1 organisms (e.g. BOTOX â ;Allergan Inc., Irvine, CA, USA; Dysport â ; Ipsen Ltd, Slough, UK and Xeomin â ; Merz Pharmaceuticals GmbH, Frankfurt am Main, Germany) [11]. These toxin products have an upper dosage limit, and their adverse events have become serious issues, speculated as after-effects of diffusion after high-dose administration [12][13][14][15]. Therefore, a preparation with greater therapeutic efficacy at lower dosages, and showing less diffusion in the body than existing drugs, has been sought. We have attempted to produce botulinum neurotoxin derived from subtype A2 (A2NTX, 150 kDa), with an amino acid sequence different from that of botulinum neurotoxin derived from subtype A1 (A1NTX, 150 kDa). Our aim is to create a product more effective and safer than the existing toxin products derived from subtype A1, and we demonstrated that A2NTX was more effective than complex of botulinum neurotoxin, hemagglutinin, and nontoxic-nonhemagglutinin derived from subtype A1 (A1 progenitor toxin, 900 kDa) and A1NTX in previous reports [16]. In this study, to investigate whether A2NTX is safer than existing botulinum toxin type A products, we compared the systemic toxicities of A1 progenitor toxin, A1NTX and A2NTX. We compared A1 progenitor toxin and A2NTX on administering the intramuscular lethal dose 50% (im LD 50 ) to mice and rats. In addition, w...
