Antibodies from Llama help detect Botulism neurotoxin

Researchers from Southwest Foundation for Biomedical Research (SFBR) have for the first time developed a highly sensitive means of detecting the seven types of botulinum neurotoxins (BoNTs) simultaneously.

 Botulinum neurotoxins (BoNTs) are the most potent natural toxins known. The family of BoNTs comprises seven antigenically distinct serotypes (A to G) that are produced by various toxigenic strains of spore-forming anaerobic Clostridium botulinum.The neurotoxin actually paralyzes the nerves so that the muscles cannot contract. This happens when the neurotoxin enters nerve cells and eventually interferes with the release of acetylcholine so the nerve cannot stimulate the muscle to contract. Unless the nerve can regenerate a new axon that has no exposure to the neurotoxin, the interference at the neuromuscular junction is permanent. This is why it takes so long to recover from botulism.

Apart from being the sole causative agent of the deadly food poisoning disease, botulism, BoNTs pose a major biological warfare threat due to their extreme toxicity and easy production. . BoNT are about 100 billion times more toxic than cyanide, and collectively, they are the only toxins in the federal Centers for Disease Control and Prevention (CDC) ‘category A’ list of potential bioterror threats alongside anthrax, Ebola virus and other infectious agents.

Interestingly, purified and highly diluted botulism toxin is being used to treat conditions that are characterized by abnormal muscle contractions. (Some examples of these conditions are torticollis, spasmodic dysphonia, achalasia, strabismus, oromandibular dystonia, cervical dystonia, and blepharospasm.).They are also used for cosmetic purposes such as treatment of wrinkles that are caused by repeated normal muscle contractions. Consequently, many people elect to have an FDA-approved formulation of the dilute toxin injected to reduce or stop wrinkles in the skin. This wrinkle treatment was first approved by the FDA in 2002. Possible side effects of this treatment include bruising, ptosis (abnormal drooping of a body part, especially the eyelid), nausea, and dysphasia (difficulty with speech), but other side effects may also occur.

A detailed investigation of the BoNT structure and function is therefore critical for designing effective specific inhibitors to counter botulism biothreat, and for the development of new therapeutics. Countermeasures to prevent and treat botulism, such as vaccines and therapeutics, are extremely limited. Consequently, the ability to detect these toxins in the environment is critically important.

 Interestingly researchers have found the Llamas produce antibodies against this neurotoxin. The llama antibodies, called single domain antibodies (sdAb) or “nanobodies,” are molecularly flexible, unlike conventional antibodies. In the new study, a llama was immunized with harmless versions of seven types of BoNT, blood taken to provide antibody producing cells. Using bioengineering techniques, the antibody genes were cloned and the resulting antibodies were tested for their ability to detect BoNT in a selection of drinks, including milk. Hayhurst and his team are continuing to study the molecular interactions of the llama antibodies to find out why they are so specific and why some of them inhibit toxins. Biosonsors that make use of these antibodies have the advantage of being used repeated without loss of function. Also, for some types of BoNT, conventional antibodies are not generally available and we are filling this biosecurity gap,” said Andrew Hayhurst, Ph.D., an SFBR virologist. Since some sdAb have been shown to have inhibitory activity and can block toxin function, they may play a role as part of a future anti-botulism treatment.

The work has been is described in the Jan. 21 issue of the journal PLoS ONE.The aim is not only to use the antibodies in BoNT detection tests, but also to understand how they bind and inhibit these fascinating molecules,” Hayhurst said. “We are also striving to improve our test by making it more sensitive such that one day it may be able to detect even trace toxin levels in patients blood. Since BoNT also have therapeutic applications with carefully controlled preparations and dosing regimens, there is also an increasing need to monitor BoNT levels in these treatments.