COMMENTARY: Proponents of stem cell research proclaim the potential that stem cells have in the treatment of a wide range of diseases. But what is the basis of these statements? In essence, why does it make sense to consider using these cells or their products as therapeutic agents?
In many diseases, the outward symptoms are caused by damage, impairment, or death of cells. This results in failure of organs forcing medical science to either artificially supplement the function of the damaged region (example kidney dialysis) or to surgically repair or replace the organ (example heart transplant).
Supplemental treatments: There are a number of medical treatments to supplement the function of diseased structures in the body. In type I (juvenile) diabetes, the beta cells of the islets of Langerhans in the pancreas do not produce the proper levels of the hormone insulin. Normally insulin is used to control the levels of glucose (sugar) in the blood stream, so the decrease in insulin results in uncontrolled levels of sugar which can cause additional problems in the body. Patients with type 1diabetes monitor the level of glucose in their blood and control the levels with diet and injections of insulin when needed. These supplemental drug treatments are effective, but there are many diseases where the necessary drugs are not available.
Organ transplants occur when a recipient’s damaged organs are replaced by organs or tissues from a living or deceased donor. A number of body organs or tissues can be replaced in this manner, but the most recognized types of organ donation involve the transplanting of heart, kidney, lungs, or skin. Successful human organ transplants have a relatively long history with the first corneal (portion of the eye) transplant occurring in 1905. Skin grafts began to be used in World War I and the first successful heart transplant occurred in 1967.
However, the number of patients needing an organ far exceeds the number of suitable organs available for transplant. This shortage of organs can result in the death of patients as they wait on the organ procurement list. Attempts have been tried to supplement the available human organs using tissues or organs from other species. These Xenografts or xenotransplants are not commonly used because of a high risk of rejection by the recipient’s body.
Scientists and physicians have attempted to use other methods to provide replacement cells to a damaged region without complete replacement of the organ. These treatments involve the use of collections of cells or small portions of an organ.
Still there are limits to the ability of cells to divide and produce replacement tissues. Small wounds to the skin heal by nearby cells migrating into the damaged region and forming scar tissue and skin. Larger regions of damage such as those caused by severe burns are often too great for the normal healing process to work. Instead physicians remove small strips of skin from undamaged regions of the body to graft into the damaged region. The strips are replaced in the donor region by the healing process.
Other regions in the body such as the brain are normally incapable of replacing cells after development before birth. Parkinson’s disease is an example of a degenerative disease of the brain. Neurons which produce the neurotransmitter dopamine die as the disease progresses. The decrease in the levels of dopamine in the brain result in uncontrolled body movements, shakiness, and sometimes progresses to paralysis. Treatment with drugs mimicking the effects of dopamine slow but do not stop the advancement of the disease, and do not work for all patients. Studies in the 1970s showed that grafts of fetal tissue rich in dopaminergic neurons could reverse the behavioral symptoms in an animal model of Parkinson’s disease. Based on a wealth of information clinical trials of transplantation of human fetal brain tissue into human patients with Parkinson’s disease began in 1987. Results of the clinical studies indicate that these cells survive and continue to produce dopamine for extended periods of time. However, there is troubling evidence that during periods of increased Parkinson’s disease disability, patients that received fetal tissue grafts may experience severe abnormal involuntary movements and postures.
From this perspective, the ability to use stem cells to generate large numbers of specialized replacement cells or to create replacement organs has the potential to dramatically improve the prognosis for patients with a wide range of illnesses.
Monday: Part 1. The collision of science and politics
Tuesday: Part 2. Basic concepts of stem cell science
Wednesday: Part 3. Cell replacement therapy
Thursday: Part 4. Future applications of stem cell treatment
Friday: Part 5. The ethics of stem cell use.
Saturday: Part 6: Medical Tourism: seeking cures around the world.
You can email me at phillyscienceguy@gmail.com or visit my website Science in my life. This series is adapted from a book manuscript in progress on The History, Science, and Politics of Stem Cells.
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