Botulinum toxin study proves possibility of remote effects

August 4, 2016 by David Tenenbaum, University of Wisconsin-Madison
In the Chapman neuroscience lab at UW-Madison, injected botulinum toxin is taken up in axons and reaches the cell body, shown in green, before being transported into different neurons, shown in red. A new study in Cell Reports is the first incontrovertible proof that this powerful toxin can jump between neurons, says senior author Edwin Chapman. Credit: Ewa Bomba-Warczak/University of Wisconsin-Madison

The botulinum toxins are among the deadliest substances on Earth, and two specific toxins—including the popular drug Botox—have multiple uses for treating many neuromuscular conditions, including frown lines, disabling muscle spasms and migraine headaches.

The botulinum toxins cancel nerve signals to the muscles, creating paralysis that can last for months. Given its extraordinary toxicity, doses are typically measured in trillionths of a gram, and targets are carefully chosen to silence only the desired motor nerves.

When Botox and related botulinum drugs entered the market, "the idea was that they are safe to use, they stay where they are injected, and you don't have to worry about going to the central nervous system and causing weird effects," says Edwin Chapman, an investigator at the Howard Hughes Medical Institute and professor of neuroscience at the University of Wisconsin-Madison.

The concern that this powerful toxin can move beyond the injection site was reinforced in 2009, when the Food and Drug Administration added a prominent warning to prescribing information "to highlight that may spread from the area of injection to produce symptoms consistent with botulism," including "unexpected loss of strength or muscle weakness. ... Understand that swallowing and breathing difficulties can be life-threatening and there have been reports of deaths related to the effects of spread of botulinum toxin."

Additionally, physicians have seen puzzling results from treatment, adds Ewa Bomba-Warczak, a doctoral candidate in neuroscience. "In many cases, after an injection for a disabling spasm of neck muscles called cervical dystonia, there is no change in muscle tone but the patient finds relief and is perfectly happy. That result can't be explained by the local effects."

In a study published today (Aug. 4, 2016) in Cell Reports, senior author Chapman, first author Bomba-Warczak and colleagues present clear evidence that toxin is moving between in a lab dish.

The study looked at mouse neurons in wells connected by tiny channels that allow growth of axons—the long fibers that neurons use to communicate. In tests of two botulinum toxins, the researchers saw toxin molecules entering the injected cell, as expected.

Once inside a neuron, botulinum toxin cleaves proteins responsible for fusion of chemical containers, known as vesicles, with the plasma membrane. This fusion event releases chemical signals that underlie communication with muscles, and the inability to fuse leads to the temporary paralysis caused by botulinum toxin.

Using antibodies to identify fragments of the damaged proteins, Chapman's group showed that toxin molecules were moving to nerve cells in wells that had not initially received the harmful molecules. "Every time one fraction of the toxin acts locally (on the first nerve cell it contacts), another fraction acts at a distance," says Chapman. "It's unknown how far they travel, which likely depends on the dose of toxin and other factors."

Co-author Jason Vevea, a UW-Madison postdoctoral fellow, produced videos showing tagged molecules of botulinum toxin moving along the axons connecting neurons.

Botulinum toxins were first described in the 1800s, and have long been a subject of research at UW-Madison. Allergan PLC, which markets four versions of botulinum toxin, reported global Botox sales of nearly $2 billion in 2015.

By finding that toxin molecules don't always stay where they are injected, Chapman says the Wisconsin study answers a long-standing question about mobility, but raises several more. "We have seen that these toxins enter neurons at the injection site, causing the desired local paralysis, but Ewa and Jason have shown unambiguously the existence of a second entry pathway that takes some of the toxin molecules to other neurons."

The research, done in a lab dish, removes variables that have plagued similar studies performed in animals, Chapman says. "We wanted to see if we could build an in vitro (in a dish) system that allows direct visualization of this putative movement, in a way that's simple, easy to interpret, and unambiguous. Do they move, or do they not?"

Chapman wonders about the effects of extraordinarily powerful toxin molecules that travel the neural networks. Local effects have, until now, been deemed the sole effects. But could part of its effects be due to the transported toxin?

These questions could be answered by genetically engineering the Clostridium bacteria that make botulinum toxin to alter the toxin's structure, Chapman says. "We may be in a position to mutate the part of the toxin that attaches to a receptor on the neuron so it can only enter the local pathway, not this new pathway we have described."

If only the local effects matter for medicine, tomorrow's versions of this ancient toxin molecule may be able to alleviate symptoms from wrinkles to severe without moving beyond the target neurons.

"I have a hard time imagining that any physician is going to want to inject something they know can move about when they have an option to use something that stays put," Chapman says. "It's an exciting prospect, supplanting a $2 billion drug with a safer drug."

Explore further: Botulinum toxin successfully treats senile entropion

Related Stories

Botulinum toxin successfully treats senile entropion

January 27, 2016
(HealthDay)—For patients with spasmodic senile entropion, injection of botulinum toxin results in a high success rate, according to a study published online Jan. 18 in the Journal of Cosmetic Dermatology.

Botox to improve smiles in children with facial paralysis

March 5, 2015
Injecting botulinum toxin A (known commercially as Botox) appears to be a safe procedure to improve smiles by restoring lip symmetry in children with facial paralysis, a condition they can be born with or acquire because ...

New insights about Botulinum toxin A

December 2, 2010
A new study by researchers at the Faculty of Kinesiology, University of Calgary, is raising questions about the therapeutic use of botulinum toxin A.

Engineered botulism toxins could have broader role in medicine

November 30, 2011
already used medically in small doses to treat certain nerve disorders and facial wrinkles — could be re-engineered for an expanded role in helping millions of people with rheumatoid arthritis, asthma, psoriasis and ...

AAN updates guidelines: Botulinum toxin for spasticity, headache, other brain disorders

April 18, 2016
The American Academy of Neurology (AAN) has updated its 2008 guidelines on the use of botulinum toxin for spasticity, cervical dystonia, blepharospasm and migraine headache, based on recent research. The guideline is published ...

New clues for battling botulism: Scientists decipher details of deadly toxin's cloaking mechanism

December 7, 2015
Scientists at the U.S. Department of Energy's Brookhaven National Laboratory and collaborators at Stony Brook University and the Institute of Advanced Sciences in Dartmouth, Massachusetts, have discovered new details about ...

Recommended for you

Perinatal hypoxia associated with long-term cerebellar learning deficits and Purkinje cell misfiring

August 18, 2018
Oxygen deprivation associated with preterm birth leaves telltale signs on the brains of newborns in the form of alterations to cerebellar white matter at the cellular and the physiological levels. Now, an experimental model ...

CRISPR technology targets mood-boosting receptors in brain

August 17, 2018
An estimated 13 percent of Americans take antidepressant drugs for depression, anxiety, chronic pain or sleep problems. For the 14 million Americans who have clinical depression, roughly one third don't find relief with antidepressants.

People are more honest when using a foreign tongue, research finds

August 17, 2018
New UChicago-led research suggests that someone who speaks in a foreign language is probably more credible than the average native speaker.

Critical role of DHA on foetal brain development revealed

August 17, 2018
Duke-NUS researchers have found evidence that a natural form of Docosahexaenoic Acid (DHA) made by the liver called Lyso-Phosphatidyl-Choline (LPC-DHA), is critical for normal foetal and infant brain development, and that ...

Automated detection of focal epileptic seizures in a sentinel area of the human brain

August 17, 2018
Patients with focal epilepsy that does not respond to medications badly need alternative treatments.

Brain response study upends thinking about why practice speeds up motor reaction times

August 16, 2018
Researchers in the Department of Physical Medicine and Rehabilitation at Johns Hopkins Medicine report that a computerized study of 36 healthy adult volunteers asked to repeat the same movement over and over became significantly ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.