Botox injection Botox injected into face muscles can travel into the brain, according to a study of laboratory rats and mice published today in the Journal of Neuroscience.
Once it reaches the central nervous system, the diluted form of the botulinum toxin can disrupt nerve cell activity, said researcher Matteo Caleo of Italy’s National Research Council, who led the project.
The study is the latest of several raising questions about the safety of the wrinkle-fighter Botox, which is made by Irvine-based Allergan.
In February, the Food and Drug Administration launched a review of Botox, citing 16 cases of deaths of patients who had received injections of the toxin.
All but one of the deaths were related to strong therapeutic doses of botulinum toxin. Even the one death that followed six weeks after an injection of weaker cosmetic-strength Botox was not caused by that treatment, Allergan said.
Allergan notes that Botox has been used safely by millions of patients over the past two decades.
Local cosmetic physicians say they have seen no problems worse than an occasional headache among Botox users, and no evidence that patients are wary of the injections. Several said that the fact that the injected toxin travels within the body has long been known, and is a reason why skilled physicians calculate safe dosages and use appropriate injection methods.
The Journal of Neuroscience gave the article the label, “Could botulinum toxin be bad for you?”
In a press release on March 26, the Society for Neuroscience, which publishes the journal, said,
Botulinum neurotoxin disrupts cell communication by destroying a protein essential to signaling between nerve cells. Matteo Caleo, PhD, of Italy’s National Research Council, and colleagues confirmed the movement of botulinum neurotoxin A by detecting the remnants of proteins it had fragmented. This evidence helped show that nerve cells at the injection site absorbed some of the botulinum neurotoxin, which was then transported across the cell and released to connected cells, where the proteins also were destroyed. The direction it traveled was opposite to that of the nerve cell’s electrical signals. These findings contradict previous research, which suggested that botulinum neurotoxin was completely degraded at the injection site and not transported beyond it.
Caleo’s team traced the movement of botulinum neurotoxins in mice and rats. The team made injections into the whisker muscles, the hippocampus, and the superior colliculus, a brain region that receives input from the eye. Using protein analysis and microscopic examination of the rodents’ brain tissue, the researchers found that, within three days, active forms of botulinum neurotoxin had migrated from the whisker muscles to the brain stem, from one hippocampus to the hippocampus on the opposite side of the brain, and from the superior colliculus back to the eye.
Brain cell activity was disrupted both where botulinum neurotoxin was injected and in some of these distant but connected sites. Caleo and his colleagues noted in particular that the effects of the botulinum neurotoxin injection on the hippocampus were still present six months later.
In March, researchers in Canada found that injected Botox migrates to nearby muscles.(This post was updated at 5:45 p.m. to add links and expand the discussion of past studies and the new Italian research.)