StemCell Therapy

Since the beginning of time, mankind has pondered the question of what it means to be alive. When, precisely, can one be considered a human being? With the advent of stem cell research, we are forced to confront this question head-on. Human embryonic stem cells have enormous medical potential; by harnessing the power of their undifferentiated state, we may be able to cure diseases and disabilities that have plagued mankind for millennia. Rather than simply treating the symptoms of debilitating conditions, we may be able to attack the diseases at their source, working from within the body itself. However, obtaining embryonic stem cells, despite the many benefits that may result, poses many new ethical questions. Embryonic stem cells are generated during the early stages of the formation of a human embryo. These cells adhere to the wall of the blastocyst and, in the process of obtaining them, the embryo is destroyed. The ethical dilemma is this; does this tiny but powerful group of cells constitute a human life, and, if so, it is justifiable to take it in order to save others?

What are Embryonic Stem Cells?

A fertilized embryo must undergo a series of divisions in order to grow. There are many different types of cells in an adult human, but, with the exception of red blood cells and lymph cells, every cell in the human body contains an identical genome. [5] If all cells contain an identical DNA sequence and originate from the same source, how does each cell know what to become? The answer lies in a population of cells known as stem cells. To be classified as a stem cell requires the possession of two key abilities

Unlike somatic cells, stem cells begin, not with a single fate, but in an undifferentiated state. This initial lack of specificity is crucial, for their division has the ability to field more unspecified cells or ones that will eventually become any cell in the organism. [3] The earliest stem cells are known as totipotent, meaning that they have the ability to differentiate into any cell in the embryo or the resulting adult. As the cells divide, they progressively lose their totipotent abilities, becoming more and more specified. The egg-sperm unit divides every 12-18 hours; first from two cells into four, then eight, then sixteen. [5] After this third cell division, totipotent cells give rise to pluripotent stem cells, which can become nearly any cell in the body. The unit is now a hollow ball known as a blastula, and with pluripotent cells adhered to the wall in a clump known as the Inner Cell Mass. The wall will become the supportive placenta as the embryo grows, with the ICM becoming the embryo itself. [7] As the pluripotent cells divide, they develop into cells called Lineage Restricted Stem Cells, then Progenitor Cells, and finally Differentiated Cells with pre-determined function. [See Figure 1] Each time the cell divides, it becomes more highly specified, and less plastic in terms of medical potential.

Why use Embryonic Stem Cells?

Because of their unique ability to generate so many different kinds of cells, and potential to reside in several areas of the human body, stem cells may eventually establish themselves as a cornerstone of 21st century medicine. Stem cell research has created an entirely new branch of medicine, called Regenerative Medicine. The specialty of this new discipline would be to repair organs or tissues affected or destroyed by age, disease or injury. [5] [6] [10] In at least one instance, experimental techniques have been highly successful. Scientists have developed large sheets of epidermal cells, which can be used to repair burns that have destroyed the full thickness of the skin. [10] Researchers are hoping to branch out and use the self-renewal and differentiating abilities of embryonic stem cells to treat diseases such as Parkinsons Disease or Type 1 Diabetes, or even paralysis resulting from damage to the spinal cord. [5] The hope is to learn to culture the cells and to manipulate their differentiation prior to inserting them into a patient. The cells would, in theory, be used to repair or re-grow the damaged tissues without being rejected by the patients immune system. In diabetic patients, the cells may be used to replace non-functioning pancreatic cells, while in paraplegic individuals the cells may replace the damaged components of the spine, allowing them to walk again.

An Ethical Mess: Are we taking a life in order to give life?

Obtaining embryonic stem cells for research purposes invariably results in the destruction of the embryo. Many individuals pose the question of whether this constitutes taking one human beings life in order to preserve the life of another. Currently, there are five major views concerning whether this ball of cells is in fact alive. Each viewpoint suggests that ones life begins at a different point in development.

Genetic View: Fertilization

Embryological View: Gastrulation A second position posits that one becomes human at gastrulation. [5] [12] Between 12 and 14 days after fertilization, the embryo begins to form germ layers, which will eventually develop into the three major tissue types found in adults. [17] Scientists view this as a turning point in development for, at the onset of gastrulation, the embryo can no longer divide to form twins. [12] If it survives, it is committed to forming a single individual. The blastula, now called a gastrula, develops three distinct layers of cells; the ectoderm, the mesoderm and the endoderm. The outermost layer, the ectoderm, will develop into the central nervous system, hair, fingernails and the epidermis of the skin. The endoderm, the innermost layer, gives rise to the lining of the digestive and respiratory tracts, and the glands such as the pancreas and liver. The mesoderm, the middle layer, is perhaps the most diverse, for it will eventually yield the muscles, the gonads, cartilage and the circulatory system, to name only a few. [17] Cells that are beginning to form the germ layers are too far along the differentiation pathway to be as useful as their predecessors. Considering the embryo to be alive only once gastrulation occurs is consistent with views in favor of Embryonic Stem Cell research. If one chooses this viewpoint, experimenting with embryos prior to this would not constitute taking a human life, for researchers would be obtaining the cells much earlier than the time of gastrulation.

Neurological View: EEG Activity The third major viewpoint is that human life begins with the acquisition of recognizable brain activity. At approximately, 24 weeks of age, there is a sufficient amount of coherence in the fetus developing brain that its activity can be seen via an electroencephalogram (EEG). [5] [18] In the United States, death is often determined by brain function. As stated in the Uniform Determination of Death Act, so-called brain death is defined as when the entire brain ceas[es] to function, irreversibly. The entire brain includes the brain stem, as well as the neocortex. The concept of entire brain distinguishes determination of death under this Act from neocortical death or persistent vegetative state. " [16] An individual whose cardiovascular and respiratory systems still function, but who produces no brain activity is considered to be dead. The fetal heart beat is present from approximately 7 weeks of gestational age, [4] but brain activity is not present until 24 weeks. This follows the logic present in US law; if we choose to define death in terms of the cessation of brain activity, we may choose to define life by its onset. This position also supports the use of stem-cell research, as the cells would be obtained months before the commencement of any recognizable brain activity.

Ecological View: Survival A fourth standpoint in terms of human life is viability. Some individuals choose to define human life as the point where the fetus is viable outside the mothers womb. [18] This has often been determined by lung function, as the respiratory system is both crucial for survival and one of the last systems to finish developing in the human fetus. Development of the lungs begins as early as week 4 of gestation, and continues until birth with the proliferation of the alveolar sacs. [8] [14] Surfactant, a compound produced in the alveoli beginning at about 34 weeks of age, reduces surface tension in the lungs and allows them to expand. Without this compound, infants have severely decreased lung function, which may prove fatal. Premature infants also have underdeveloped brain and immune function, which makes them highly susceptible to both apnea and infection as well as a host of other health problems. [14] Historically, many infants born before 28 weeks of age were unable to survive. [5] However, with the continued development of neonatal intensive care and cardio-pulmonary life support, the cutoff line for viability has become increasingly blurred. One is now forced to question whether a neonate born at 25 weeks of age with severely impaired brain and body function and kept alive only with assistance of machines is truly living.

The Birth View

Conclusion

Stem cells hold a power never before seen in medicine. If properly controlled, they may allow us to fight diseases that are now considered incurable. Their use, however, remains highly controversial, owing to the destruction of embryos in the process. Advocates against embryonic stem-cell research and use argue that the tiny ball of cells inside the blastula is alive. These individuals take the Fertilization viewpoint, maintaining that a human, no matter how small, is still a human. To them, the use of embryonic stem cells, even to save many others, can never justify the destruction of a human life. Supporters of embryonic stem cells maintain that zygotes are not truly human prior to gastrulation, brain function or even birth itself. Use of the inner cell mass in its earliest stages does not constitute ethical wrongdoing. The cells are obtained so early that the mass does not yet possess any human qualities, such as differentiated tissues or brain function. These individuals also point out that the majority of the blastocysts being used would not survive to begin with, and that anti-stem cell groups should see that the ends justify the means. Clearly stem cells have many potential benefits for mankind, but at the moment they are surrounded by a controversy that is unlikely to resolve itself any time soon. In the future, perhaps we will find a way to manipulate differentiated cells to have undifferentiated properties, thereby avoiding the ethics of embryonic stem cell use. However, until that day arrives, we must continue to ask ourselves the question of what it means to be human.

More:
Life and Death in Terms of Embryonic Stem Cells

This entry was posted on October 23, 2015 at 7:45 pm and is filed under Death by Stem Cells. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed. |