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Biological regeneration has been studied over the years, in salamanders, and biological imitations of life. Through research on the mitotic capabilities of certain animals, to the DNA and hormones that make regeneration possible, scientists are slowly finding a way so that humans can regenerate lost or missing limbs, or grow organs used to save millions of lives in the future. Because being able to reproduce a limb or body part is dependent on nerves, scientists have found it vital to perform especial experimental procedures to find a way to prevent difficult regenerated nerves from inhibiting the regeneration process. The medicinal leech, a worm-like creature once used by doctors to bleed patients, now is being used to draw clues on how a common protein may help promote neural regeneration. A specific enzyme or protein, called nitric oxide synthase, or NOS, is activated when parts of the nerve cell are damaged in the medicinal leech. This particular Hirudinean leech is a three-inch-long invertebrate known for its ability to regenerate its neural connections.
Scientists hope that one day their findings may be applied to research in human spinal regeneration. Purdue's studies show that NOS in the leech is activated at the site of injury within minutes after axons or nerves are severed. Axons are the long "arms" of a nerve cell that carry impulses away from the cell body toward a target cell. NOS remains active well beyond 48 hours after the injury to start neural reconstruction. Conducting follow-up studies to identify what information this molecule provides at a cellular level, they see how these functions might help the leech's nervous system set itself up to allow regeneration to occur. This same enzyme NOS, also found in humans, produces a "signaling" molecule that sends chemical messages throughout the body to incite certain chemical reactions.
The enzyme found in leeches is very much like the human NOS, and it may serve a similar function in both species. However, the drawback is that nerve regeneration in higher systems is not complete as it is in medicinal leeches and such less complex creatures. By analyzing how nerves regenerate in a simple system, scientists may begin to find clues to facilitate regeneration in vertebrates. After the problems of regeneration and axonal regrowth are solved for humans, the next issue scientists are interested in, is the creation of man-made tissues or organs, known as neo-organs.
There are two procedures being currently tested. In the first, more tested experimental procedure, the scientist injects or places a given molecule, such as a growth factor or a synthase, into a wound or an organ that requires regeneration. These molecules cause the patient's own cells to migrate into the wound site, and then turn into the right type of cell and regenerate the tissue. In the second, and more ambitious experimental procedure, the patient receives cells-either his or her own or those of a donor. Such procedures are considered highly experimental, but there is biological substantiation that such procedures should be able to regenerate organs.
The proof can be found in any expectant mother's womb, where a small group of undifferentiated cells finds the way to develop into a complex individual with multiple organs and tissues with vastly different properties and functions. Now scientists are looking for a way to eventually replicate that process observed in early fetuses in fully developed humans. A critical challenge in engineering neo-organs is feeding every cell. Tissues more than a few millimeters thick require blood vessels to grow into them and supply nutrients.
Studies have shown that cells already in the body can be coaxed into producing new blood vessels. Folkman and his fellow scientists recognized this possibility almost three decades ago in studies aimed, ironically, at the prevention of cellular growth in the form of cancerous tumors. Folkman perceived that developing tumors need to grow their own blood vessels to supply themselves with nutrients. That work is now being exploited by tissue regeneration engineers.
Many angiogenesis-stimulating molecules are commercially available in recombinant form, and animal studies have shown that such molecules promote the growth of new blood vessels that bypass blockages in, for example, the coronary artery. An additional, practical issue is how best to administer the substances that would shape organ regeneration. Along with the exciting new technology and research being carried on to regenerate nerve tissue, grow limbs, and hopefully one day, grow organs for replacement purposes, there are ethical debates raging in the scientific arena following the topic of regeneration, in whichever country it goes. Scientists will be able to replace degenerating organs, find a cure for sclerosis of the liver, replace deteriorating hearts, and help reconstruct failing bones in osteoporosis. However, philosophers often ask, that if our lives can be elongated by replacing failing body parts, then is there any motivation to accomplish and achieve before we die? There is always the plaguing question of "Where are the boundaries?" When is it acceptable to lengthen people's lives by growing organs?
The philosophers maintain that if there is no end to our existence, there is no motivation to fill it, to accomplish, to do good "before we go. " We will able to live longer, replacing those parts that age along the way. A handful of laboratory experiments has provided clues, at the cellular level, to the processes of aging. The implications have fueled hopes that medical advances will slow our decline, extending longevity well beyond the century mark. Still, researchers have rounded up at least one or two likely suspects in the war on decrepitude and senility. Oxidizing agents in our bodies, created as we metabolize food, cause our cells to degrade in the same way that rust eats away at a car. New drugs, some of which may be cousins of the vitamins we now eat with voracity, may combat the effects of these potent chemicals.
A harshly restrictive diet might also slow our inevitable decline. But to replace body parts? What would happen to society if we could all live to 100, much less 120 and up? Could it accommodate a massive population of elderly people? What would a "family" mean?
The average life span in the U. S. alone has risen from 47 to 76 since 1900, which is a 62 percent increase. But what if humans suddenly found that a simple organ transplant or taking a special protein to regenerate depleting organs-a wonder antioxidant or some other metabolic miracle-that would immediately allow the world to live much longer? But research to extend life is exactly where cures may be found for some of the most debilitating illnesses the elderly face: Alzheimer's, Parkinson's, heart disease, liver and kidney disease, and cancer. Also, the posed question is that if the science fulfills its promise, will the emerging new society transform work, family and social institutions in ways we cannot even begin to imagine?
Bibliography 1. "Stem-cells, Transcriptions Factors, & Control of Ageing. " Life-Extension & Control of Ageing Program. < web 1 December 2001. 2. Steinberg, Douglas. "Stem Cells Tapped to Replenish Organs. " The Scientist. Vol. 14 (Nov. 27) 3. Dinsmore, Charles E. , et. al.
A History of Regeneration Research. Cambridge University Press, 1992.
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