Scientists Say Man May Be Able to Regrow Lost Limbs, Organs

Science fiction over the last 40 years has been replete with themes of amputated arms and legs growing anew. One author in the late 1960s even described how regeneration replaced the need for organ transplants.

But scientists are taking such concepts seriously because the technology that may turn such fiction into fact is beginning to appear on the horizon. The goal: elimination of cumbersome artificial limbs and organ transplantation.

Dr. Susan Bryant of the University of California, Irvine, pointed to broken bones, hair, nails and skin as the only structures that humans currently regenerate, and predicted, “Someday, I think humans will be able to regenerate more complex structures.”

Her prediction, however, is based not on views of human evolution but on laboratory experiments involving animals capable of regenerating lost limbs and other body structures.

She thinks that the genetic secrets governing limb and nerve regeneration in lower animals ultimately will be discovered and used to help people in need of new body parts.

Bryant said the human liver possesses some capabilities of regaining its original size by enlarging after surgical removal of a lobe. But she added that enlargement is not true regeneration because the missing lobe is not reproduced.

The developmental biologist said some scientists think that the superior position of mammals on the evolutionary ladder probably caused genes that could play a role in regeneration to switch off after embryonic development.

“There is evidence in salamanders that when a limb develops in an embryo and regenerates again in the adult (after amputation), the animal is using the same mechanisms.

“The implications are, that in amphibians, developing limbs and regenerating limbs are very much part of the same process. And since humans possess the same capability to develop structures, they must also possess the ability to regenerate,” she said.

Research under way at the University of California, San Francisco, is slowly cracking some of the mysteries of collagen molecules, the chains of amino acids that form skin, bones, ligaments, cartilage and many other structures.

Biochemist Rajendra Bhatnagar thinks that eventually he may explain how electric fields play a role in stimulating growth and differentiation of these molecules, providing new clues on how human tissue organizes into complex structures.

Studies at UC San Francisco and other research centers across the country show that certain sections along molecular chains of collagen may be responsible for development of different physiological structures.

But Bhatnagar and his team are trying to show how electric fields influence collagen’s formation of these highly ordered tissues, possibly stimulating genetic information stored during the embryonic stage of an animal’s development.

“Collagen molecules tend to line up when an electrical field is applied. And even though the research is very preliminary, it is my hypothesis that fiber formation is determined by the direction of the electrical field,” he said.

In the laboratory, Bhatnagar is charging collagen samples with electricity comparable to charges found in the electric fields of human bone.

Because the human body is a storehouse of electricity, charged particles contained in bone may aid in its repair in cases of breakage or fracture, Bhatnagar said.

The biochemist cites as encouraging recent advances the rapid healing of broken bones with external application of electric fields, a strong hint that collagen molecules are being stimulated by electricity.

But perhaps even more exciting to the scientist is the recent New York experiment in which a frog regenerated a severed limb when electrodes were applied to the wound.

Bhatnagar said that people maintain throughout life the genetic information to form new organs or limbs and cited growing evidence that children may be capable of regenerating missing fingertips.

The trick now is figuring out how to switch on the genes that govern organ or limb regeneration in instances when people require new ones.

“We have to figure out how to make mammals reuse the information that’s already there,” said UC Irvine’s Susan Bryant.

Part of the answer may be found in work also under way at the UC Irvine Developmental Biology Center involving nerve regeneration--experiments that might lead to treatments for victims of Alzheimer’s and Parkinson’s diseases.

Scientists are finding that, contrary to long-held views, damaged nerves in the brain and spinal cords of mammals can make more than simple attempts to regenerate.

“We really don’t know all of the answers, but there is reasonably good evidence that nerve fibers have the capability to regrow. They make abortive efforts to regrow,” said UC Irvine developmental biologist Ronald Meyer.

He added that recent experiments have shown that fetal rat brain tissue transplanted into adult rats proved that the hosts accepted the transplant without rejection and continued to regenerate healthy tissue afterward.

“The brain, as it turns out, is rather privileged in accepting grafts. Tissue transplanted in other parts of the body are rejected unless it’s very closely matched.”

He said his experiments may ultimately show that the very chemical environment in which nerve cells exist may be preventing complete nerve regeneration in cases of injury or aging.