The Fascinating Search for New Medicines
By Awake! correspondent in Britain
What do rubber, cocoa, cotton, and painkillers have in common? All may be obtained from plants. In addition to sugar and oxygen made by means of photosynthesis, green plants also produce an extraordinary array of substances from other basic chemical building blocks. These secondary chemicals are what give each plant its distinctive properties.
THE sting of a nettle, the sharp flavor of an apple, and the delicate fragrance of a rose are all due to different combinations of chemical substances manufactured by the plants themselves. Thus, what might seem to be a single product is in fact often a very complex mixture.
Nature’s Chemical Factories
Consider the characteristic smell of cocoa. Did you know that scientists have so far discovered 84 different volatile chemicals that combine to make up this unique aroma? The contents of cacao beans are extremely complex, and much effort has been expended in recent years to identify them. And that is just one natural product.
Cholesterol is a fatty substance, perhaps best known for its possible connection with human heart disease. Yet, in some plants it is the starting point for making a vital group of chemicals called steroids. Steroids include vitamin D, hormones (such as cortisone), and medicines such as the anti-inflammatory betamethasone. Diosgenin, a steroid used in the manufacture of oral contraceptives, is produced by certain types of wild yam. Cortisone, on the other hand, is manufactured from hecogenin, a natural steroid extracted from sisal leaf pulp after fiber making. Many of today’s new drugs were first isolated from plant tissue.
Plants and Man
Although man’s use of synthetic drugs is a modern medical development, plant extracts have been used as cures for common ills for thousands of years. Early Assyrian records describe the use of the common anemone to alleviate pain. And Egyptian medical papyri from the time of the Pharaohs reveal a widespread use of medicinal plants.
The World Health Organization has recorded the use of about 20,000 medicinal plants worldwide. In Britain alone an estimated 6,000 to 7,000 tons of herbs are used annually as ingredients in some 5,500 different herbal products, and in the United States, it has been reckoned that over half of all doctors’ prescriptions are for medicines derived from plants.
Finding New Medicines
With as many as 250,000 known species of plants in the world, each possessing a potentially unique chemistry, scientists constantly look for clues to find useful medicines. One of the obvious ways is to study how people treat ailments using plants growing in their locality.
The discovery of cocaine started with the observation that chewing coca leaves deadened hunger pangs and eased fatigue. By isolating and modifying the structure of the cocaine molecule, chemists produced a synthetic derivative for use as a local anesthetic. If your dentist has given you an injection to “freeze” part of your jaw to save you from a painful experience, then you may well have benefited from this research.
Much valuable information on the use of plants is still filed away in botanical collections. Scientists who spent over four years examining 2.5 million specimens in the Gray Herbarium and Arnold Arboretum of Harvard University were able to pinpoint more than 5,000 plant species previously overlooked as potential sources of medicines.
Another line of inquiry compares the chemical contents of plants. If one species contains useful compounds, related species may also be valuable. When work on a north Australian tree, the Moreton Bay chestnut, isolated castanospermine, a poison displaying antiviral activity, botanists searching for related trees suggested looking at the South American Alexa.
Sometimes clues can be misleading and then yield unexpected results. It was claimed, for example, that extracts from the Madagascar periwinkle could treat diabetes. Canadian research workers began testing it, but to their surprise the periwinkle extract suppressed the immune system by lowering production of white blood cells. This gave doctors the idea of testing the extract against leukemia, a cancer of the white blood cells.
Eventually about 90 substances were isolated, of which two, known as vincristine and vinblastine, proved medically useful. They are present in the plant in such small amounts that about one ton of plant material is needed to produce .07 ounces [2 g] of vincristine. Today these compounds and their derivatives provide a chemotherapy used worldwide in the treatment of childhood leukemia.
In the late 1950’s, the U.S. National Cancer Institute initiated a 25-year screening program, during which 114,000 plant extracts from 40,000 species were tested for antitumor activity on cancer cultures. About 4,500 of these produced a noticeable effect, worthy of further study. But consultant pharmacognosist Dr. W. C. Evans points out: “It is highly unlikely that broad-spectrum anticancer drugs will actually be found” as a direct result of such research, important as it is. Cancers vary enormously, and only a few fast-growing cancer-cell cultures were used in these tests.
New Medicines From Old Plants
Well-known plants are providing researchers with more food for thought. Ginger, for example, is now being used as an antiemetic, particularly effective against motion sickness.* More significantly, ginger could prove to be valuable in relieving sufferers of the tropical parasitic disease schistosomiasis (bilharzia). Tests on infected schoolchildren in Nigeria, using tablets of ginger powder, have stopped the occurrence of blood in their urine and lowered the schistosome egg count.
Researchers have hardly begun the task of examining the vegetable kingdom in the search for more medicines. Even those plants relatively well-known still retain many secrets. Licorice is now in demand since chemicals discovered in it are effective anti-inflammatory agents and their derivatives can give relief to some persons who suffer from arthritis. Scientists are also looking at the common garden pea for antifungal and antimicrobial effects.
The wanton destruction of plant species in certain areas of the world, before those plants have been recorded, means that the search for new medicines must continue on apace. Careful chemical analysis of plants and their genetic conservation remains a top priority, even for plants that are well-known. But there is one puzzle still to be solved: Of what use are many of these extraordinary chemicals to the plants themselves? Why, for example, does the purslane plant produce such a high concentration of noradrenaline, a hormone found to be essential to human welfare?
Really, our knowledge of the complexities of plant life is still extremely limited. But what we do know points to an overall design, with credit to a Grand Designer.
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Ginger is being used as an antidote to motion sickness