Medicines From Plants - Vinblastine, Vincristine and L-dopa
The Madagascar periwinkle is an attractive flowering plant that contains the anti-cancer chemicals vinblastine and vincristine. These chemicals are used as chemotherapy drugs. The pods of the velvet bean are covered by soft hairs. The beans contain L-dopa, a very 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. 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 one meter tall.
The sap of the Madagascar periwinkle 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.
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
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, and a low red blood cell count, resulting in anemia. There may occasionally be nerve damage, possibly due to the effect of the medicines on the microtubules in the nerve cells. Vincristine is more likely to cause nerve damage than vinblastine.
How Cells Divide and How Chemotherapy Works
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. The scientific name of the velvet bean is Mucuna pruriens.
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 and 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 dopamine is unable to cross the blood-brain barrier. However, L-dopa, which the body converts into dopamine, can penetrate the blood-brain barrier.
Synthetic L-dopa is a standard medication for treating Parkinson’s disease and improving the patient’s quality of life. L-dopa is also known as levodopa. It's often administered with a helper medicine called carbidopa, which prevents L-dopa from breaking down in the body before it gets to the brain.
Velvet Beans and Parkinson's Disease
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.
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.
Unlike the Madagascar periwinkle, velvet beans can be eaten to obtain the medication inside them. 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.
Can Velvet Beans Help Parkinson's Disease?
In 2004, the result of an 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. They found that the bean powder started to work faster (34.6 minutes versus 68.5 minutes) and worked for 37 minutes longer. The results of this experiment are interesting. However, clinical trials with larger sample sizes and bean powders containing different doses of L-dopa are needed in order to confirm and clarify the results.
If you have Parkinson’s disease, it's very important that you don't add velvet beans to your diet or make any medication changes without consulting your doctor.
Fava or Broad Beans and L-dopa
Fava beans are called broad beans. They contain L-dopa, although much less than velvet beans. Fava bean sprouts, pods, stems and leaves contain more L-dopa than the fava 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 purchase than synthetic chemicals. However, the dose of a natural medicine is often unknown when plant parts are eaten, unless a chemical analysis is performed. Plant parts or extracts may also contain toxins in addition to the 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.
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