Last week, scientists reported the discovery of a new antibiotic in the journal Nature. The antibiotic was isolated from bacteria growing in the soil right here in New England. This got me thinking about all of the various medicines that come from nature, which you can read about in WBUR’s Commonhealth blog.
What makes this antibiotic especially exciting is the way it was discovered. The scientists used a technique that allowed them to screen bacteria for antibiotics without growing them in culture. Because only a small percentage of bacteria have been grown in culture, this technique opens the door to finding antibiotics from bacteria and other microbes we don’t even know about.
The antibiotic, called teixobactic, comes from a bacterium that was found in a sample of soil from Maine. It’s not the only antibiotic that comes from a bacterium. In fact, many of our antibiotics come from bacteria and other microbes, and many of our medicines come from nature. This is one way we benefit from the diversity of species on this planet.
I was recently teaching a class on biodiversity to college students. To get the students thinking about how we benefit from species richness, I asked the class to name a couple of medicines that derive from nature.
I thought this would be an easy question. To my surprise, the class (of 250 students) was silent. This was unusual – I usually have more trouble keeping the class quiet rather than coaxing answers from them. Finally, after maybe 20 seconds (a long time in a large lecture hall), a hand shot up. “Marijuana!” the student proudly exclaimed.
I was taken aback. Not because weed was mentioned in a college classroom. And not because the student was incorrect – she was of course correct. Marijuana comes from the plant Cannabis and it has some useful medicinal properties, for example to treat nausea caused by cancer chemotherapy, and fatigue, appetite loss, and pain associated with AIDS. As a result, there is continued debate over its use.
But that’s not the point. The point is that while the class was hard-pressed to come up with more than one medicine derived from nature, the reality is just the opposite: It’s difficult to think of a medicine that doesn’t ultimately come from nature.
If apples and carrots are nature’s toothbrush, grapes are nature’s jellybeans, and raisins are nature’s candy, then certainly plants, animals, fungi, and microbes are nature’s medicine cabinet.
Perhaps the most famous example is penicillin. In 1928, as the story goes, Alexander Fleming accidently left the lid off of one of his petri dishes in which bacteria were growing. The open lid allowed fungus to grow in the dish. Fleming noticed that the bacteria were killed in an area around the fungus. He reasoned that the fungus secreted a substance that killed the bacteria, and called it penicillin after the name of the fungus.
Some time after its discovery, penicillin was synthesized in the lab. And then scientists were able to play with its structure so that it could be used against different kinds of bacteria. Derivatives of penicillin include ampicillin, methicillin, and cephalosporins. But, at the heart of all of these widely used antibiotics is the chemical structure that ultimately comes from nature.
Like penicillin, aspirin was not invented by a scientist working quietly away in a lab. Instead, it too is naturally occurring. Since ancient times, it was known that an extract of the bark of the willow tree could be used to treat pain and fever. Even Hippocrates was aware of its medicinal properties.
The active ingredient in the bark is salicylic acid, which is also found in shrubs of the genus Spiraea. It is from Spiraea that we get the name aspirin. Aspirin is not only used to treat headaches, but also, in the form of “baby aspirin,” is used by millions of people to prevent heart attacks and strokes.
Aspirin and penicillin are two of the most widely used drugs in the world today. And the list of medicines from nature goes on and on. From the Pacific yew tree, we get taxol, used to treat breast, ovarian, and lung cancers; from foxglove, a common flower in English gardens, we get digitalis, used to treat congestive heart failure; from the rosy periwinkle, a flower from Madagascar, we get vincristine and vinblastine, which have changed the prognosis of certain types of cancers; and from the bark of the South American cinchona tree, we get chloroquine, long the mainstay in the prevention and treatment of malaria.
And there are organisms we are only just beginning to investigate and understand. Cone snails, known for their beautiful shells and deadly venom, are potential sources of pain medicine far more powerful than opium (which comes from poppies). The venom from the South American rattlesnake is being studied for its ability to alleviate pain. This wouldn’t be the first drug to come from snakes: The venom of the lancehead viper in Brazil served as the chemical template for ACE inhibitors, used to treat high blood pressure.
From nature, we are discovering not only medicines used to treat diseases, but also substances useful in diagnosis. For example, when surgeons remove a cancer, it is often difficult to tell where the cancer ends and healthy cells begin. Enter the Deathstalker scorpion. From its name, you wouldn’t think that it would provide us with any benefit at all. But, it was found that its venom can bind specifically to cancer cells. Dr. Jim Olson and his colleagues at the Fred Hutchinson Cancer Research Center in Seattle took advantage of this property and engineered the venom so that cancer cells can be visualized during surgery. This “tumor paint” may one day revolutionize cancer surgery.
The importance of biodiversity to human health has been extensively and thoughtfully explored by Dr. Eric Chivian and Dr. Aaron Bernstein of Harvard’s Center for Health and the Global Environment in their recent and authoritative Sustaining Life: How Human Life Depends on Biodiversity.
This pharmacopeia raises a question: Why would other organisms make so many compounds that are useful as medicines in humans?
One answer has to do with defense. Bacteria and fungi defend themselves from other bacteria and fungi, so it is perhaps not surprising that they are rich sources of antibiotics.
Plants and other organisms need to protect themselves too, in some cases from mammals. Over time, they have evolved chemicals that serve just this purpose. In small doses, or modified in specific ways, they end up being beneficial since they have already evolved to interact with our cardiovascular, immune, or nervous systems. Medicines, after all, are poisons in small doses.
Another answer is that all living things, because they share a common ancestor, are in many ways more similar than they are different. The fact that bacteria in a sample of soil from a field in Maine may help us to fight infections that have evolved resistance to other antibiotics serves as an important reminder of the unity of life.
© James Morris and Science Whys, 2015