STEM CELLS: HAS SCIENCE GONE TOO FAR?

Advances in stem cell research have led some to predict cures for a host of illnesses. But not everyone shares the excitement. Why is there so much controversy surrounding stem cells?

“The stem cell debate has led scientists and nonscientists alike to contemplate profound issues, such as who we are and makes us human beings”

                                 MEDICAL MARVEL, ETHICAL MINEFIELD


Kris has Type 1 diabetes. Her diseased pancreas no longer produces insulin. Now imagine if Kris could go to a doctor and have new cells, specially cultured in a laboratory, transplanted into her body to replace damaged pancreatic cells.

As these new cells became functional, Kris could gradually discontinue insulin therapy and return to normal health. Until recent times potential cures would have sounded like science fiction, but now some researchers believe that they are a possibility. Why so? Because in 1998, scientists found a way to culture large numbers of cells called HUMAN STEM CELLS.

These stem cells can grow to become almost any of the over two hundred different types of cells found in the human body, including pancreatic cells.

Dolly the sheep was the first mammal cloned from an adult cell. Scientists implanted the nucleus of a cell from the mammary gland of an adult sheep into an enucleated egg cell.
According to a report prepared by the National Institutes of Health in the United States, stem cells may hold the key to replacing cells lost in many devastating diseases. These include, Parkinson’s disease, end-stage kidney disease, liver failure, and cancer, to name just a few.

 Stem cells can also give rise to blood, and they may even make blood banks obsolete, it is claimed. In fact, doctors have been using stem cells for many years to treat certain blood disorders.

These treatments have usually involved transplantation of bone marrow, which is rich in blood-forming stem cells, but now doctors prefers to harvest stem cells taken from circulating blood. Because stem-cell therapies hold promise of regenerating healthy new tissues, they come under the general designation “regenerative medicine.”

Certain aspects of this fledgling science, however, are highly controversial. Many people, including a number of scientists, feel that the exploitation of human stem cells –particularly those derived from either embryos or fetuses –shows a disregard for the sanctity of human life. The issue has become so hot, in fact, that is has been likened to an ‘ethical and political minefield.’

Because stem cell advocates predict miracle cures for a host of conditions, the following article takes a closer look at the different kinds of stem cells, how they are derived, and why the subject is so controversial.

                                        WHY THE CONTROVERSY?


 In the hands of a trained craftsman, a lump of soft clay can be formed into practical any shape. Embryonic stem cells are the living equivalent of that piece of moist clay; they have the prospective to give rise to virtually all of the over 200 cell types making up the human body. How do they do this? Consider what happens to a newly fertilized egg cell.

 Soon after fertilization an egg cell begins to divide. In humans about five days of cell division results in a minute ball of cells called a BLASTOCYST. It is essentially a hollow sphere that is composed of a shell-like outer cell layer and a small cluster of about 30 cells called the inner cell mass, which is attached to the inside wall of the sphere. The outer cell layer becomes the PLACENTA; the inner cell mass, the human embryo.

 At the blastocyst stage, though, the cells of the inner cell mass have not yet begun to specialize into specific cell types, such as nerve, kidney, or muscle cells. Hence, they are designated stem cells. And because they give rise to virtually all the different cell types in the body, they are said to be PLURIPOTENT. To make sense of the excitement and mystery surrounding stem cells, let us see what the researchers have done thus far and what their goals are, beginning with embryonic stem cells.

                                            [1]           EMBRYONIC STEM CELLS

 The report Stem Cells and the Future of Regenerative Medicine states: “In the last three years, it has become possible to remove these [human embryonic] stem cells from the BLASTOCYST and maintain them in an undifferentiated state in cell culture lines in the laboratory.” Simply put, embryonic stem cells can be cultured so as to produce an unlimited number of identical copies of themselves. Embryonic stem cells extracted from mice, first cultured in 1981, have produced billions of duplicate cells in the laboratory.

Because all these cells remain undifferentiated, scientists hope that with the right biochemical triggers, stem cells could be directed to develop into virtually all the cell kinds that may be needed for tissue replacement therapy. Simply put, stem cells are seen as a potential source of unlimited ‘spare parts,’

In two animal studies, researchers coaxed embryonic stem cells into becoming insulin-producing cells, which were then transplanted into diabetic mice. In one study the symptoms of diabetes were reversed, but in the other the new cells failed to produce enough insulin. In similar studies, scientists have had partial success in restoring neural function in spinal cord injuries and in correcting Parkinson’s disease symptoms. Those studies provide promise but not definitive evidence, that similar treatment could be effective in humans.” But why is research on human embryonic stem cells so controversial?

                                                                             WHY THE CONCERN?

The main focus of concern is that the process of extracting embryonic stem cells essentially destroys the embryo. This deprives a human embryo of any further potential to develop into a complete human being.

 For those who believe that the life of a human being begins at the moment of conception, ESC [embryonic stem cell] research violates tenets that prohibit the destruction of human life and the treatment of human life as a means to some other end, no matter how noble that end might be.

Where do laboratories get the embryo from which stem cells are extracted? Generally from in vitro fertilization clinics, where women have provided eggs for in vitro fertilization. Leftover embryos are usually either frozen or discarded. One clinic in India discards over 1,000 human embryos each year.

While research on embryonic stem cells continues, some investigators are focusing their efforts on a much less controversial form of stem cell –the ADULT STEM CELL.

                                                        [2]           ADULT STEM CELLS

 The adult stem cells is an undifferentiated [specialized] tissue, such as bone marrow, blood and blood vessels, the skin, the spinal cord, the liver, the gastrointestinal tract, and the pancreas. Initial research suggested that adult stem cells were much more limited in scope than their embryonic counterparts. However, later findings in animal studies suggest that certain kinds of adult stem cells may be able to differentiate into tissues other than those which they came.

 Adult stem cells isolated from blood and bone marrow, called HEMATOPOIETIC STEM CELLS [HSCs], have the ability to self-renew continuously in the marrow and to differentiate into the full complement of cell types found in blood.

 This type of stem cell has already been used to treat leukemia and a number of other blood disorders. Now some scientists also claim that HSCs appear to give rise to nonblood cells such as liver cells and cells that resemble neurons and other cell types found in the brain.

Using another type of stem cell derived from the bone marrow of mice, researchers in the United States appear to have made another break through. Their study, published in the journal Nature, showed that these cells seem to have all the versatility of embryonic stem cells.

 In principle these adult stem cells could do everything expected of embryonic stem cells but these cells are rare and difficult to identify. On the other hand, any medical benefits they may yield will not involve the destruction of human embryos.

                                                          [3]   EMBRYONIC GERM CELLS

Besides adult and embryonic stem cells, embryonic germ cells have also been isolated. Embryonic germ cells are derived from the cells in the GONADAL ridge of an embryo or a fetus, which give rise to eggs or sperm. [The gonadal ridge becomes the ovaries or testes.] Although embryonic germ cells are different in many ways from embryonic stem cells, both are pluripotent, or able to give rise to virtually all cell types.

This potential makes pluripotent cells very attractive candidates for the development of unprecedented medical treatments. However, the excitement over such potential therapies is tempered by the controversy centering on the source of these cells. They are derived either from aborted fetuses or from embryos. Thus, obtaining these cells involves fetal and embryo destruction.

                                                       HEALTH RISKS AND REGENERATIVE MEDICINE
Whatever form of stem cell is used, therapies will still have serious drawbacks –even if scientists master the processes that yield tissues for transplantation.  

One of the major obstacles is the rejection of foreign tissue by the recipient’s immune system. The present solution is to administer potent drugs that suppress the immune system, but such drugs carry serious side effects. Genetic engineering may avoid this problem if stem cells can be altered so that tissues derived from them do not appear foreign to their new host.

Another possibility might be to use stem cells taken from the patient’s own tissues. In early clinical trials, hematopoietic stem cells have already been used in this way to treat LUPUS. Diabetes may yield to similar therapies, as long as the new tissue is not susceptible to the same autoimmune attack that may have caused the disease in the first place.

People with certain heart diseases may also benefit from stem cell therapies. One proposal is that at-risk patients donate their own stem cells in advance so that these could be cultured and later used to replace diseased cardiac tissue.

In wrestling with the problem of immune rejection, some scientists have even proposed cloning patients but allowing the clones to develop only to the BLASTOCYST stage, when embryonic stem cells can be harvested. Tissues cultured from these stem cells would be genetically identical to the donor-recipient. But besides being morally repugnant to many people, such cloning may be futile if the intent is to cure a genetically based disease.

Summing up the immune problem, the National Academy of Science stated: “An understanding of how to prevent rejection of transplanted cells is fundamental to their becoming useful for regenerative medicine and represents one of the greatest challenges for research in this field.”

Embryonic stem cell transplantation also carries the risk of tumor formation, in particular a tumor called a teratoma, meaning ‘monster tumor.’ This growth may comprise a variety of tissues, such as skin, hair, muscle, cartilage, and bone.

During normal growth, cell division and specialization follow a strict genetic program. But these processes can run awry when stem cells are severed from the blastocyst, cultured in viro, and later injected into a living creature. Learning to master artificially the enormously complex processes of cell division and specialization is yet another major hurdle facing researchers.

                                                                      NO IMMINENT CURES

The report Stem Cells and the Future of Regenerative Medicine states: “Because of a misunderstanding of the state of knowledge, there may be an unwarranted impression that widespread clinical application of new therapies is certain and imminent. In fact, stem cell research is in its infancy, and there are substantial gaps in knowledge that pose obstacles to the realization of new therapies from either adult or embryo-derived stem cells.” Clearly, there are more questions than answers.

Some scientists are even “bracing themselves for a backlash when treatments fail to materialize, says a New York Times report. Stem cell science aside, medicine has made great strides in many areas in recent decades. Yet, as we have seen, some of these advances raise complex moral and ethical questions.
So where can we turn for sound guidance on such matters? What is more, as research becomes more sophisticated and expensive, therapies and medications often reflect that cost. Some researchers have already estimated that stem cells therapies may cost hundreds of thousands of dollars per patient.

Yet, even now millions of people are unable to keep up with escalating medical costs and insurance premiums. So who really will benefit if and when the stem cell revolution arrives at the clinic? Only time will tell. What we can be sure of, however, is that no therapy conceived by man will eliminate sickness and death.

                                                           HOW A CLONE CAN BE MADE

In recent years scientists have cloned a variety of animals. In 2001 a laboratory in the United States even attempted, albeit unsuccessfully, to clone a human. One way that scientists make clones is through a process called NUCLEAR TRANSFER.

First, they extract an unfertilized egg cell from a female and enucleate the cell, or remove its nucleus, which contains the DNA. From the body of the animal to be cloned, they obtain a suitable cell, such as a skin cell, the nucleus of which contains its owner’s genetic blueprint. They insert this cell [or just its nucleus] into the enucleated egg and pass an electric through it. This fuses the cell with egg cytoplasm. With its new nucleus, the egg now divides and grows as if it were fertilized, and a clone of the creature from which the body cell was taken begins to develop.

The embryo can then be implanted in the womb of a surrogate mother, where, in the rare instance all goes well. It will grow to term. Alternatively, the embryo may be kept only until the inner cell mass can be used to obtain embryonic stem cells that can be kept in culture. Scientists believe that this basic process should work with humans. In fact, the above-mentioned attempt to clone as human was performed with a view to acquiring embryonic stem cells. Cloning for this purpose is called THERAPEUTIC CLONING.
The stem cell debate had led scientists and nonscientists alike to contemplate profound issues, such as who we are and what makes us human beings.

                                                     THE DISEASE WE DO NOT HAVE TO HAVE

 Osteoporosis is the disease we do not have to have. It is largely preventable. Yet it is predicted that by 2020, one in three hospital beds will be occupied by women with fractures. A report by Osteoporosis Australia shows that the disease, which makes bones porous and brittle, is more prevalent than high cholesterol, allergies or the common cold.

 It costs more than diabetes or asthma. And the death rate in women from hip fractures is greater than the incidence of all female cancers combined. Estimates show that in Australia half the women and a third of the men will sustain a fracture from osteoporosis during their lifetime. The best defense is to build peak bone mass in the first three decades of life through exercise and adequate calcium intake.

 The risk of suffering from osteoporosis can be greatly reduced by avoiding smoking and excessive alcohol or caffeine consumption. Positive habits include engaging in regular exercise and consuming foods rich in calcium and vitamin D.       


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