Medicines From Plants: Vinblastine, Vincristine, and L-dopa
Plants That Contain Medicinal Chemicals
The Madagascar periwinkle is an attractive flowering plant that contains vinblastine and vincristine. These chemicals are used as chemotherapy drugs. The pods of the velvet bean are covered by soft hairs, which gives the plant its name. The beans contain L-dopa, a helpful chemical in the treatment of Parkinson’s disease.
The Madagascar periwinkle and the velvet bean are just two of the large number of plants that have been found to contain medicinal chemicals. There are almost certainly many more plants in nature that have undiscovered health benefits, which is a powerful argument in support of their protection.
Plants containing medicines are sometimes grown as crops. The beneficial chemicals are obtained by an extraction process and concentrated to make a drug. In other cases, scientists investigate natural chemicals to discover their structure and then produce synthetic chemicals that are identical to the natural ones. Sometimes researchers are able to improve the properties of natural chemicals and make them even more effective medications. In all these situations, however, a plant species is essential for the development of a new medicine.
The Madagascar Periwinkle
The Madagascar periwinkle is native to Madagascar and India but is now grown in many countries as a garden plant. It has also escaped from gardens and grows as a weed. The red, purple, pink, or white flowers often have a center which is a different color from the rest of the flower. Madagascar periwinkles have glossy green leaves and may grow up to a meter tall.
The sap of the plant has a milky appearance and is poisonous. It contains vinblastine, vincristine, and many other alkaloids. Researchers are discovering that many of these alkaloids are biologically active inside the human body.
Vinblastine and vincristine are both used to treat cancer. The medications are extracted from Madagascar periwinkles, but the yield is quite low. Researchers are exploring ways to increase the amount of medicinal chemicals made by the plant. They are also investing efficient methods to make the drugs synthetically.
It's important to note that some medicinal plants, including the Madagascar periwinkle, mustn't be eaten to self-treat a disease because they are poisonous. In addition, the beneficial substance in a plant may need to be concentrated or modified before it's helpful. It may also need to enter the body via a method other than ingestion.
Vinblastine, Vincristine, and Cancer
Vinblastine and vincristine have very similar chemical structures. Although they work in the same general way, their abilities aren't identical. Each is helpful for specific types of cancers.
Vinblastine is used to treat disorders such as Hodgkin’s disease (or Hodgkin's lymphoma), non-Hodgkin's lymphoma, and testicular cancer. It's also used to treat a condition called Langerhans cell histiocytosis, or LCH. Langerhans cells are part of the immune system and help the body to fight infections. In LCH, too many immature Langerhans cells are made. As the cells collect, they form tumors and damage organs.
Vincristine is used in the treatment of several types of leukemia (cancer of the white blood cells) and lymphoma (cancer of the lymph cells, or lymphocytes). It's also used to treat Wilms' tumor, which is a type of kidney cancer, as well as some kinds of brain cancer.
Chemotherapy and Microtubules
How Do Vinblastine and Vincristine Work?
Cells contain a supporting network of protein tubules, which are known as microtubules. Microtubules also play a vital role in the movement of cell parts and in the process of cell division.
The nucleus of a cell contains chromosomes. Each chromosome is made of a DNA molecule attached to protein. DNA is the genetic material of cells. Before a cell divides, every chromosome in the nucleus is replicated, enabling each daughter cell to have an identical set of chromosomes.
At first, the two copies of each chromosome are joined together. Microtubules separate the paired chromosomes and pull the former partners to opposite ends of the cell during a process called mitosis. Once the chromosomes have reached their destination, the cell divides down the middle.
Vinblastine and vincristine stop microtubule formation during mitosis. This prevents mitosis and cell division from taking place. This effect is strongest in cells that have a high rate of division, such as cancer cells. Therefore vinblastine and vincristine can act as chemotherapy drugs.
Chromosomes Joined to Microtubules (Spindle Fibers) During Mitosis
How Cells Divide and How Chemotherapy Works
Vinblastine and Vincristine Side Effects
Unfortunately, in addition to affecting cancer cells, vinblastine and vincristine affect other cells that have a high rate of cell division. These include cells in the lining of the intestine, the cells in the bone marrow that produce blood cells, and the cells in the hair follicles. Interference with these cells produces side effects of the cancer treatment.
Possible vinblastine or vincristine side effects include:
- constipation and other gastrointestinal problems
- hair loss
- a low platelet count, which can cause increased bleeding
- a low white blood cell count, which can lead to increased infections
- a low red blood cell count, resulting in anemia.
The drugs may occasionally cause nerve damage, possibly due to their effect on the microtubules in the nerve cells. Vincristine is more likely to cause nerve damage than vinblastine.
The velvet bean is a climbing plant that is native to tropical areas in the Caribbean, Africa, and India and is cultivated in various parts of the world. It’s a member of the legume family, a plant group that contains beans and peas. Its scientific name is Mucuna pruriens. It's sometimes known as cowhage, the hell fire bean, or another name.
Velvet beans are very variable in appearance. The flowers range from white to purple in color. The pods that contains the seeds (or beans) are covered with orange, brown, grey, white, or black hairs. These hairs can produce a severe itch when human skin touches them. The seeds inside the pods are shiny and may be black, brown, maroon, or white. They may also have a mixture of colors and appear mottled.
Like many other beans, velvet beans are a good source of protein, but they are potentially toxic. If they are used for food they have to be soaked for a long time. In addition, the boiling water has to be changed several times during the cooking process to remove the toxins. In some parts of Central America the beans are roasted and then ground to use as a coffee substitute.
Parkinson's Disease Symptoms
L-Dopa and Parkinson's Disease
In people with Parkinson’s disease, brain cells that make a chemical called dopamine are damaged and destroyed. The amount of dopamine in the brain therefore decreases. As a result, the affected person can't control or coordinate their muscle movements properly.
At the moment we don’t know for certain why dopamine-producing cells are damaged in people suffering from Parkinson’s disease. Dopamine administered to patients is unable to relieve their symptoms because the chemical is unable to cross the blood-brain barrier. L-dopa, which the body converts into dopamine, can penetrate the blood-brain barrier, however.
Synthetic L-dopa is a standard medication for treating Parkinson’s disease and improving the patient’s quality of life. It's also known as levodopa. It's usually administered with a helper medicine called carbidopa. Carbidopa prevents levodopa from breaking down in the body before it gets to the brain and therefore reduces the required dose. This may in turn reduce nausea, a possible side effect of levodopa administration.
L-dopa is toxic at high concentrations and can have unpleasant or dangerous side effects. Some of these effects, including hallucinations, anxiety, and confusion, are the result of changing brain chemistry.
L-Dopa in Velvet Beans
Velvet beans contain L-dopa. The chemical is sometimes present in large amounts. The amount of L-dopa in velvet beans depends not only on the cultivar of bean but also on the environmental conditions in which the bean plants are grown.
Unlike the Madagascar periwinkle, velvet beans can be eaten to obtain the medication inside them. In addition, the medication may be concentrated enough to be helpful. A big problem with using velvet beans to obtain L-dopa is that the amount of medication in the beans varies, however. A person doesn’t know how many beans to eat in order to obtain an effective or a safe dose of L-dopa or how much L-dopa he or she is actually ingesting.
Velvet Beans and Parkinson's Disease
Velvet beans have traditionally been used for Parkinson's disease—or at least for symptoms resembling those of the disease—in some cultures. There hasn't been much scientific research related to the benefits of the beans, however.
In 2004, the result of one investigation involving velvet beans and Parkinson's disease patients was published in the British Medical Journal. Only eight patients took part in the investigation. The researchers compared the medicinal effects of a synthetic L-dopa/carbidopa mixture with a velvet bean powder in a double blind experiment. In this type of experiment, neither the test subject nor the person administering a substance knows whether the substance is the medication or a placebo. The researchers discovered that the bean powder started to work faster (34.6 minutes versus 68.5 minutes) and worked for 37 minutes longer than the L-dopa/carbidopa treatment.
The results of the experiment are very interesting. Clinical trials with much larger sample sizes and bean powders containing different doses of L-dopa are needed in order to confirm and clarify the results, however. If the bean powder is helpful, it would be interesting to identify the chemical in the bean that serves the same function as carbidopa. Unfortunately, as far as I know, no recent investigations related to the effect of velvet beans on Parkinson's disease have been performed.
Since velvet beans contain L-dopa, they may affect the symptoms of Parkinson's disease. If you have the disease, it's important that you consult your doctor before adding the beans to your diet. If L. dopa intake from all sources is either too low or too high, problems can result. In addition, other chemicals in velvet beans may interfere with certain medications.
Fava or Broad Beans and L-Dopa
Fava beans are also called broad beans. They contain L-dopa, although much less than velvet beans. It would still be a good idea for a patient taking prescribed L-dopa supplements to ask their doctor about the advisability of eating fava beans. The bean sprouts, pods, stems, and leaves reportedly contain more L-dopa than the unsprouted beans.
Some people suffer from a genetic problem called favism and can't eat fava beans. These people are unable to make enough of an enzyme called glucose-6-phosphate dehydrogenase. The disorder is therefore sometimes called glucose-6-phosphate dehydrogenase deficiency, or G6PD deficiency. In this disorder the red blood cells burst when exposed to certain stimuli, including the ingestion of fava beans.
Advantages and Precautions for Natural Medicines
Medicines are often discovered in plants, analyzed, and then synthesized in a laboratory later. Destruction of the Earth’s plant species will decrease our chances of discovering new medicines.
Natural medicines can be useful in disease treatment and may be cheaper to obtain than synthetic chemicals. The dose of a natural medicine is often unknown when plant parts are eaten, however, unless a chemical analysis is performed. Another potential problem is that plant parts or extracts may contain toxins in addition to a medicine.
Like synthetic medicines, natural medicines can cause side effects, interact negatively with other medications inside a person’s body, or be dangerous for people with additional medical problems besides the one being treated. Therefore it’s very important to follow a doctor’s advice before and during the use of natural medicines.
- The U.S. National Library of Medicine contains vinblastine information.
- The Cancer Research UK website has more information about vinblastine.
- The U.S. National Library of Medicine contains facts about vincristine injections.
- Information about vincristine can also be found at the Mayo Clinic website.
- The University of California, San Francisco, describes Parkinson's disease medications, including L-dopa.
- Mucuna pruriens in relation to Parkinson's disease is described in the Journal of Neurology, Neurosurgery and Psychiatry (a publication of the British Medical Journal)
- The University of Maryland website has facts about Parkinson's disease and its treatment.
© 2011 Linda Crampton