Science Looks at a Common Herbal Medication that Poisons as Well as Cures
Discover now a little herbal history and what scientists are recently doing with an herbal plant that poisons as well as cures.
Some Foxglove History
The German-Swiss physician and alchemist “Paracelsus” (1493-1541) is credited for his contribution in establishing the role of chemistry in medicine. He is best known for his quoting of what science refers to today as the basic tenant of toxicology: “All things are poison and nothing is without poison; only the dose makes a thing not a poison.”
This quote is oft repeated in a condensed form of: “The dose makes the poison”—meaning that a substance that contains toxic properties can cause harm only if it occurs in a high enough concentration. Other meanings point out more broadly that giving anything in a high enough dose is a poison, such as water for example.
One example of an herbal medication that poisons as well as cures depending on the dose, and that has made the news lately, is the famous decorative plant Digitalis purpurea—known more commonly as Foxglove.
Foxglove is a biennial belonging to the snapdragon family, of which during its first year of life produces a rosette of green, fleshy, simple leaves that are otherwise unremarkable in appearance. However, in its second year, blooming scapes appear that yield 3-inch long, tubular purple flowers that are quite attractive and grown by many for its aesthetic qualities.
Foxglove reputedly takes its name from old English "foxes glofa" based on an old myth that foxes used the flowers of the plant to magically sheath their paws as they stealthily made their raids into the poultry yards of rural folk during the night.
The scientific name for foxglove gets its first part from the Latin word “Digitalis” for either its finger-shaped (i.e. digit) flowers or for the observation that the finger easily slips into the flower like a glove and thereby pays some reference to its older folklore origins. The second part of its Latin name “purpurea,” refers to its distinctive purple coloration.
The use of foxglove as a medicinal herb goes back hundreds of years. Primarily, it was first used as a purging agent by herbal healers due to that giving enough of the plant effused in a tea resulted in bouts of violent vomiting. The belief was that vomiting helped rid the body of whatever was ailing it. It was also used in the treatment of open wounds as a paste applied to the affected areas.
Later on, physicians began to investigate the medicinal abilities of foxglove when it was rumored that aside from the rough purgative properties and sometimes accidental deaths from taking foxglove, that it also appeared to be a remedy for Dropsy.
“Dropsy” is what edema (swelling via fluid retention) of the legs, ankles and face used to be called back in the early days of medicine. Medically, one of the causes of fluid retention is a failing of the muscle of the heart to beat strongly enough, which results in congestive heart failure due to a buildup of fluids in the body. Herbal healers back in the day did not know about the cardiac causes of dropsy, but what they did know was that one of the effects of taking foxglove is increased urination, which alleviated the excessive swelling.
For a fascinating historical account by one physician in 1785 while investigating foxglove as a potential medicine, here is a Google Books read titled “An Account of the Foxglove and Some of its Medical Uses & Etc.” that talks about patient deaths, turkey tests, and other observations made using foxglove as a treatment for disease.
Foxglove’s Role in Modern Medicine
Today, however, the use of the foxglove plant has come a long way and is a common medicine known as “Digoxin”—that takes its name from foxglove’s Latin genus Digitalis—that is used as a first line of defense against chronic heart related ailments.
Digoxin works by increasing the force of contraction of the heart muscle by inhibiting the activity of an enzyme called ATPase that controls movement of calcium, sodium, and potassium into heart muscle cells. Calcium controls the force of contraction; hence, inhibiting ATPase results in increasing the amount of calcium entering the myocardial cells that make up the muscle fibers leading then to an increase in the force of contractions.
Incidentally, Digoxin also slows electrical conduction between the atria and the ventricles of the heart and is useful in treating abnormally rapid atrial cardiac rhythms such as atrial tachycardia, atrial fibrillation and atrial flutter.
Foxglove Research Today
As it turns out, “cardiac glycosides” are the active component in Digoxin that gives foxglove its curative properties. However, extracting cardiac glycosides from foxglove is a laborious and time-consuming process that scientists want to improve upon.
Such an improvement is the topic of a recent study announced from a University of Buffalo news piece discussing how researchers are trying to unlock the mystery of exactly how foxglove makes its cardiac glycosides.
“How plants synthesize many natural products is largely unknown,” says University of Buffalo biologist Zhen Wang, an assistant professor of biological sciences. “I want to understand how we can harness the power of nature to make the process of producing medicinal compounds more efficient and sustainable. Foxgloves make these powerful compounds, but it takes two years to do so, and they don’t make them in a very large quantity. How can we improve this process?”
According to the University of Buffalo news, because each foxglove plant makes only a little bit of the chemical, farmers must grow the crop in huge quantities.
“It takes two years, from the time you plant the seed to the time the leaves are ready to harvest, and then you have to dry it in the silo,” says Wang. “Then, the plant is crushed into powder, and the compound is extracted and purified using chemical processes.”
To gain a better understanding of how cardiac glycosides are made, Wang’s research team has been busy comparing the characteristics of cardiac glycosides found in two foxglove species: Digitalis purpurea, the attractive purple flower typically grown in gardens, and Digitalis lanata, which is the species grown for developing Digoxin due to it has significantly higher levels of the desired compounds. The results of their findings thus far can be found published in two recent papers detailing the characteristics of cardiac glycosides in the two species of foxglove.
If Wang’s team can figure out, step by step, how foxgloves make cardiac glycosides, then biologists could possibly engineer fast-growing microbes, such as yeast or harmless strains of bacteria, to produce those same type of cardiac glycosides using the same processes as plants use.
The advantage of this is that it would make synthesizing cardiac glycosides much quicker in greater amounts, and at less cost. However, the significance of their work goes beyond making increased amounts of the active ingredient of foxglove at a cheaper cost, but also extends to the manufacture of other bio-compounds in nature that have medicinal value.
“We can learn from nature,” Wang says. “We can study all of the available compounds that are found in the plants and then come up with our own design of compounds that are safer and more effective. That’s why I think it’s important to not just focus on the current drug digoxin, but to expand our focus to all the compounds in the same class, the cardiac glycosides.”
Advice on Growing Foxglove
The thing to know about growing foxglove is that it is a biennial plant, which means they do not bloom until their second year. Come the second year they produce beautiful, bell-shaped flowers, and then die. However, they do reseed easily if the surrounding soil is hospitable to their growth. Therefore, if you want flowering foxglove plants every year, plant them two years in a row.
Foxglove grows in full sun or medium shade and does best in a moderately fertile, well-drained soil that receives some water during the summer. Foxgloves can be grown from seed in containers in May or June. Seed germination is easy and seedlings can usually be transplanted to a more-permanent container after three or four weeks. The first-year plants are then transplanted to their final location in the garden during the early Fall so that they can establish themselves before cold weather arrives.
Because of the potential for exposing yourself to the toxic cardiac glycosides, it is recommended to handle the plant with gloves on. Furthermore, you should be aware that sometimes growers or wildflower scavengers mistake comfrey (Symphytum officinale) for foxglove (and vice versa) due to their similar bell-shaped purple flowers.
If you have any experience on growing foxglove or know of an instance of adverse exposure to the plant, please let us know in our comments section below.
This story has been reviewed by Dr. Inaam Schneider, MD of Schneider Medical Group. According to U.S. News Health, Dr. Inaam Schneider is an internist in Raleigh, North Carolina. She received her medical degree from Wayne State University School of Medicine and has been in practice for more than 20 years.
Dr. Schneider adds: "Digitalis ( Foxglove) is one of the earliest plants identified to have “medicinal “ value. It later evolved for the treatment of what is now referred to as Congestive Heart Failure ( CHF). In modern medicine, Digoxin was used in the treatment of CHF and the treatment of rapid heart rhythm such as Atrial Tachycardia, atrial fibrillation/ Flutter. It has fallen out of favor since more advanced and less toxic meds have been developed."
Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Today, with a background in farming and an avid home gardener, Timothy continues writing about science with a focus on the connection between plant biology and gardening for healthy living. For continual updates about plants and health, you can also follow Timothy on Twitter at TimBoyerWrites.
1. “Foxglove plants produce heart medicine. Can science do it better?” by Charlotte Hsu for the University of Buffalo, UBNow news; Published April 13, 2020.
2. “Profiling and structural analysis of cardenolides in two species of Digitalis using liquid chromatography coupled with high-resolution mass spectrometry” Baradwaj Gopal Ravi Et al; Journal of Chromatography A; Available online 22 January 2020; https://doi.org/10.1016/j.chroma.2020.460903
3. “High-resolution tandem mass spectrometry dataset reveals fragmentation patterns of cardiac glycosides in leaves of the foxglove plants” Baradwaj Gopal Ravi, Et al; Journal of Chromatography A; https://doi.org/10.1016/j.dib.2020.105464
4. “Plant of the Week: Foxglove (Latin: Digitalis purpurea)” University of Arkansas, Division of Agriculture Cooperative Extension Service
5. “An Account of the Foxglove and Some of its Medical Uses & Etc.” 1785; Google Books