Fabrication, characterization and evaluation of a new designed botulinum toxin-cell penetrating peptide nanoparticulate complex

BACKGROUND

To have a better and longer effect, botulinum neurotoxin (BoNT) is injected several times in a treatment course, which could increase side effects and cost. Some of the most cutting-edge strategies being investigated for proteins to their physiologic targets involve the reformulation of BoNT based on peptide-based delivery systems. For this purpose, cell-penetrating peptides (CPPs) are of particular interest because of their capacity to cross the biological membranes.

OBJECTIVES

A short and simple CPP sequence was used as a carrier to create nanocomplex particles from BoNT/A, with the purpose of increasing toxin entrapment by target cells, reducing diffusion, and increasing the duration of the effect.

METHOD

CPP-BoNT/A nanocomplexes were formed by polyelectrolyte complex (PEC) method, considering the anionic structure of botulinum toxin and the cationic CPP sequence. The cellular toxicity, and absorption profile of the complex nanoparticles were evaluated, and the digit abduction score (DAS) was used to assess the local muscle weakening efficacy of BoNT/A and CPP-BoNT/A.

RESULTS

The provided optimized polyelectrolyte complex nanoparticles had a 244 ± 20 nm particle size and 0.28 ± 0.04 PdI. In cellular toxicity, CPP-BoNT/A nanocomplexes as extended-release formulations of BoNT/A showed that nanocomplexes had a more toxic effect than BoNT/A. Furthermore, the comparison of weakening effectiveness on muscle was done among nanoparticles and free toxin on mice based on the digit abduction score (DAS) method, and nanocomplexes had a slower onset effect and a longer duration of action than toxin.

CONCLUSION

Using PEC method allowed us to form nanocomplex from proteins, and peptides without a covalent bond and harsh conditions. The muscle-weakening effect of toxin in CPP-BoNT/A nanocomplexes showed acceptable efficacy and extended-release pattern.

Optimization of the rat digit abduction score (DAS) assay: Evaluation of botulinum neurotoxin activity in the gastrocnemius lateralis, peronei, and extensor digitorum longus

The mouse digit abduction score (DAS) assay is commonly used to measure muscle flaccidity-inducing effects of botulinum neurotoxin (BoNT) in vivo. Adapting the assay to rats has been challenging, as injection of onabotulinumtoxinA (onaBoNT-A) into the gastrocnemius muscle, as performed in mice, or into the tibialis anterior leads to sub-optimal sensitivity of the test (Broide et al., 2013). To optimize the experimental design of the rat DAS assay, we evaluated the effects of research-grade, purified, native BoNT serotype A1 (BoNT-A) in three muscles: the gastrocnemius lateralis, peronei, and extensor digitorum longus using female animals. Following injection, animals were tested daily for the digit abduction and body weight.

BoNT-A caused dose-dependent inhibition of digit abduction when injected into the gastrocnemius lateralis or peronei. BoNT-A was six-fold more potent when injected into the peronei in comparison to the gastrocnemius lateralis. As injection of BoNT-A into the extensor digitorum longus muscle resulted in an all-or-none digit abduction response and therefore prevented calculation of the ED₅₀, it was considered unsuitable for the rat DAS assay. At equipotent doses, peronei- and extensor digitorum longus-injected animals showed normal body weight gain, while those injected with BoNT-A into the gastrocnemius lateralis gained less weight in comparison to vehicle-treated controls.

Thus, injecting the peronei muscles of female rats offers optimized conditions for evaluating the biological properties of BoNTs in the rat DAS assay; for assessing the potency, onset, and duration of action across natural and recombinant BoNT in a robust and reproducible manner.

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BoNT-A was tested in the DAS following injection into three muscles of female rats.

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DAS linked to the extensor digitorum longus injections lacks dose-dependency.

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Gastrocnemius injections inhibit digit abduction, but with an effect on body weigh.

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Peronei injections are linked to higher potency and no effects on body weight.

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Using the peronei in female rats are optimized conditions in the rat DAS assay.