Botulinum toxin: From poison to cosmetics and medication

Recently I had a chat with a longtime friend who I had not met for a few years. She just turned into a “Fil-Sen” (Filipino senior citizen). She does not look like a senior citizen though. One of the things that we talked about was that she was thinking of a “botox” treatment to correct her few facial lines. So I decided to write on this topic.

Botox is a brand name of botulinum toxin type A. Botulinum toxin is a neurotoxic protein produced by Clostridium botulinum, anaerobic Gram-positive spore-forming bacteria that can thrive in water, soil, and mammals’ intestinal tract. The growth of Clostridium botulinum is favored in moist, low acid, low salt and oxygen-free environment. Without these conditions, the bacteria transform into spores that remain dormant until the spores can survive in an environment that is favorable to growth. Botulinum toxin can be destroyed by thorough cooking, but the bacterial spores are heat-resistant and can endure in boiling water for a certain period of time.

As one of the most poisonous biological substances, botulinum toxin can cause botulism, a severe and life-threatening disease. Food-borne botulism may result from eating home-preserved or canned foods which are contaminated with the toxin-producing bacteria. Infant botulism may occur due to the low-acid digestive system of the infant, allowing the spores to grow and make the toxin. Wound botulism may arise from infection with spores that later germinate, producing the toxin.

Strains of Clostridium botulinum produce various types of toxins with a high degree of similarity in the sequences of amino acids among them. Types A, B, E and F were found to be associated with botulism in humans. Botulinum toxin is produced as a single biologically inactive polypeptide (protein) chain. Activation of the protein gives rise to a heavy chain and a light chain with molecular masses of about 100 kilodaltons (kDa) and 50 kDa, respectively; the two chains are joined by a single disulfide bond between two amino acid cysteine units. Keywords: Botulinum toxin, Clostridium botulinum, clinical applications, adverse effects.

The heavy chain binds to the receptors on the cell surface and promotes the translocation of the toxin into the cell’s cytoplasm by endocytosis. The light chain has protein-degrading activity that allows it to destroy a protein (i.e., SNAP-25 for botulinum toxin type A or synaptobrevin for botulinum toxin type B) needed in the fusion of the synaptic vesicle (neurotransmitter vesicle) with the plasma membrane. This action blocks the release of the neurotransmitter acetylcholine from synaptic vesicles, preventing neurotransmission and causing muscle paralysis.

Some medical conditions are characterized by involuntary and uncontrollable muscle contractions. Several decades ago researchers discovered that injection of overactive muscles with regulated doses of botulinum toxin type A diminished muscle activity due to blockage in the release of acetylcholine from the nerve endings. Later researchers found that botulinum toxin type A could smooth out wrinkles by paralyzing the muscles that cause the wrinkles, and it could also inhibit sweating. Now botulinum toxins are in clinical use for various therapeutic and cosmetic applications. These include drugs that were approved by the US FDA, such as: OnabotulinumtoxinA for strabismus, blepharospasm, cervical dystonia, upper limb spasticity, urinary incontinence with overactive bladder due to neurologic disease, chronic migraine, and severe axillary hyperhidrosis; OnabotulinumtoxinA (Cosmetic) for glabellar lines and crow’s feet; AbobotulinumtoxinA for cervical dystonia and glabellar lines; IncobotulinumtoxinA for blepharospasm, cervical dystonia and glabellar lines; and RimabotulinumtoxinB for cervical dystonia.

Botulinum toxin is injected directly into the affected muscle or skin. The dose of the toxin is measured in units of biological activity; one unit is equivalent to the mean lethal dose (LD50) of toxin in mouse assay, that is, the amount of toxin that kills 50 percent of a test group of mice. A newly developed botulinum toxin assay makes use of nerve cells grown in a dish. 

As a precaution, people should take a rest after toxin injection. Strenuous physical activities and massage of the injected body parts are to be avoided for a few days to prevent toxin dislodgment and movement to adjacent muscles. The effect of botulinum toxin usually lasts for a few months and recovery occurs with the growth of nerve terminals. Follow-up injections at regular intervals are needed to maintain the desired effects. Individuals who initially respond well may eventually develop tolerance to the toxin due to the production of antibodies.

The possible side effects of botulinum toxin injections listed in the US FDA approval records include discomfort or pain at the injection site, muscle weakness, muscle pain, neck pain, headache, tiredness, dry mouth, dry eyes, drooping eyelids, double vision, blurred vision, allergic reaction, swallowing difficulty, breathing problem, and hoarseness or change or loss of voice. The more serious side effects may be due to the spread of toxin from the injection site.

The study of Coté and colleagues (Journal of the American Academy of Dermatology 2005, vol. 53, pp. 407-415) showed that for therapeutic use of botulinum toxin type A, there were 217 serious adverse effects that included 28 deaths out of 406 cases reported to the US FDA. For cosmetic use, there were 36 serious adverse effects out of 1,031 reported cases; the serious adverse effects were headache, muscle weakness, focal facial paralysis, flu-like syndrome, allergic reaction and swallowing difficulty. The more serious adverse effects for therapeutic use were attributed to higher doses and/or underlying diseases, e.g., patients with heart disease may have suffered from complications after toxin injections. Regarding cosmetic use, the adverse effects were mainly due to the lack of adherence to the FDA-approved label, particularly the recommended maximum dose. Deviations from FDA recommendations for injection site, handling, dilution, administration and storage were also noted in that study, which may have contributed to the serious adverse effects.

Now let me go back to facial lines and my friend’s contemplation to be “botoxed.” Other than being age-related, environmentally induced or genetically influenced, facial lines and wrinkles reflect the emotions that people have mostly gone through in life; i.e., sadness, anger, disgust, fear, surprise, happiness, etc. So far, the use of botulinum toxin for cosmetics to correct facial lines seems reasonably well tolerated by most people who have no complicated underlying diseases, provided that the indications for the use and management are strictly adhered to by licensed and experienced healthcare professionals. But then, cosmetic treatment with botulinum toxin may cause smiling and other facial expressions, and the purse as well, to be under tight control.

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Elsie C. Jimenez, a biochemist and molecular biologist, is professor emeritus at the University of the Philippines Baguio. E-mail at [email protected].