Analysis of Motor Neurons Differentiated from Human Induced Pluripotent Stem Cells for the Use in Cell-Based Botulinum Neurotoxin Activity Assays.

Botulinum neurotoxins (BoNTs) are potent neurotoxins produced by bacteria, which inhibit neurotransmitter release, specifically in their physiological target known as motor neurons (MNs). For the potency assessment of BoNTs produced for treatment in traditional and aesthetic medicine, the mouse lethality assay is still used by the majority of manufacturers, which is ethically questionable in terms of the 3Rs principle. In this study, MNs were differentiated from human induced pluripotent stem cells based on three published protocols. The resulting cell populations were analyzed for their MN yield and their suitability for the potency assessment of BoNTs. MNs produce specific gangliosides and synaptic proteins, which are bound by BoNTs in order to be taken up by receptor-mediated endocytosis, which is followed by cleavage of specific soluble N-ethylmaleimide-sensitive-factor attachment receptor (SNARE) proteins required for neurotransmitter release. The presence of receptors and substrates for all BoNT serotypes was demonstrated in MNs generated in vitro. In particular, the MN differentiation protocol based on Du et al. yielded high numbers of MNs in a short amount of time with high expression of BoNT receptors and targets. The resulting cells are more sensitive to BoNT/A1 than the commonly used neuroblastoma cell line SiMa. MNs are, therefore, an ideal tool for being combined with already established detection methods.

Botulinum toxin type D blocks autonomic cholinergic synapses in humans: discussion of a potential therapeutic use.

Based on epidemiological data it was believed that botulinumtoxin type D (BT-D) may not block human cholinergic synapses. We wanted to investigate BT-D's effect on the autonomic cholinergic synapse in humans. For this, we compared in four volunteers intraindividually the hypohidrotic effect of intradermal BT-D and BT-A in Minor's iodine starch sweat test. Altogether, we studied BT-D in doses of 4, 8, 16 and 32MU and BT-A in doses of 2, 4, 8 and 16MU at weekly intervals throughout a period of 13 weeks. All BT doses were diluted in 0.2 ml 0.9% NaCl/H2O. Overall 704 data points were collected. Combined over all four subjects and all four doses BT-D's hypohidrotic effect intensity was half of BT-A's. BT-D's effect peaked around 5 weeks, BT-A's around 7 weeks. BT-D's effect duration was around 12 weeks, of BT-A's was around 14 weeks. For both BT types the hypohidrotic effect was dose dependent. BT-D, when injected intradermally, can block autonomic cholinergic synapses in humans. Compared to BT-A, BT-D's effect intensity was half and its effect duration was some 2 weeks shorter. With its weaker and shorter effect BT-D does not seem to promise therapeutic effects superior to BT-A.