Botulinum Toxin Complex Serotype B-Okra Exerts Systemic Toxicity via the Oral Route by Disrupting the Intestinal Epithelial Barrier.

Botulinum toxin (BoNT) causes flaccid paralysis by blocking the release of neurotransmitters. BoNTs associate with neurotoxin-associated proteins to form medium and large progenitor toxin complexes. The large progenitor toxin complex serotype A-62A (L-PTC/A-62A) specifically targets intestinal M cells for invasion, whereas large progenitor toxin complex serotype B-Okra (L-PTC/B-Okra) is mainly taken up by enterocytes and exhibits higher toxicity via the oral route. Hemagglutinin (HA) is a neurotoxin-associated protein that promotes BoNT absorption from the intestine and has carbohydrate-binding and barrier-disrupting activities. In this study, we established an in vitro reconstitution and purification system for recombinant L-PTC/B-Okra and created a recombinant L-PTC/B-Okra mutant rL-PTC/B-KA with carbohydrate-binding activity but not barrier-disrupting activity. rL-PTC/B-KA showed significantly reduced oral toxicity. Our results demonstrate that the B-Okra toxin disrupts the epithelial barrier of enterocytes and exerts oral toxicity.