|
"[Embryonic] stem cells could be used to make up for the
deficits in brain and pancreas cells that cause Parkinson's
disease or diabetes. It is the only present hope that those who
suffer from these ailments have" (emphasis added).
-- David Baltimore, Nobel laureate and President, California
Institute of Technology, Wall Street Journal, 7/30/01.
"With [embryonic stem cells], I have no doubt I can be cured. I
have virtually no doubt I could walk again as my spinal cord has
not been cut and my injury is confined in one very small area.
It's my big chance."
-- Christopher Reeve, actor and executive director, The
Christopher Reeve Paralysis Foundation, This is London, 2/27/02
Is embryonic stem cell research really "the
only present hope" for those suffering debilitating diseases?
Such extravagant claims are not substantiated in the scientific
literature. Following are three areas – Parkinson's, spinal cord repair and
diabetes -- often referred to as examples of the successful use
of embryonic stem cells and their future therapeutic potential.
But even at their most successful, embryonic stem cells are
eclipsed by adult stem cells in the treatment of disease.
|
Parkinson's Disease |
|
Adult Stem Cells Injection of growth
protein into brains of Parkinson's rats caused their neural stem cells to
grow, migrate to the site of damage, and begin to replace missing nerve
cells. Eighty percent (80%) of the rats received a benefit from the
treatment, with no tumor formation.
Reference
J. Fallon et al.; "In vivo induction of massive proliferation,directed
migration, and differentiation of neural cells in the adult mammalian
brain," Proc. Natl. Acad. Sci. USA 97, 14686-14691; December 19, 2000
|
Embryonic Stem Cells
Parkinson's rats
injected with mouse embryonic stem cells showed a modest benefit for just
over 50% of the rats, but one-fifth (20%) of the rats died of brain tumors
caused by the embryonic stem cells.
Reference
L.M. Bjorklund et al.; "Embryonic stem cells develop into functional
dopaminergic neurons after transplantation in a Parkinson rat model," Proc.
Natl. Acad. Sci.USA
www.pnas.org/cgi/doi/10.1073/pnas.022438099
(PNAS Early Edition) Jan 8, 2002 |
|
Spinal Cord Regeneration |
|
Adult Stem Cells In animal studies, several labs have shown that
adult stem cells are capable of re-growth and reconnection in spinal cord
injury, allowing functional recovery.
Adult stem cell transplants "promote functional recovery of paraplegic
adult rats and long-distance motor axon regeneration in their completely
transected [severed] spinal cords," and showed "dramatic functional
improvement and anatomical repair" (Ramon-Cueto et al; 2000).
Others, using either transplanted adult stem cells or injection of normal
growth proteins to stimulate existing adult stem cells, achieved re-growth
of neurons and re-myelination (sheathing) of neurons.
Eighteen-year old Melissa Holley, a paraplegic patient with a severed
spinal cord, has been treated with her own immune cells, and has regained
movement of her toes and bladder control. (no peer-reviewed paper yet; Globe
and Mail (Toronto), June 15, 2001]
References
M. Sasaki et al., "Transplantation of an acutely isolated bone marrow
fraction repairs demyelinated adult rat spinal cord axons," Glia 35, 26-34;
July 2001
A. Ramon-Cueto et al., "Functional recovery of paraplegic rats and motor
axon regeneration in their spinal cords by olfactory ensheathing glia,"
Neuron 25, 425-435; February 2000.
M.S. Ramer et al.; "Functional regeneration of sensory axons into the
adult spinal cord," Nature 403, 312-316; January 20, 2000S. Shihabuddin et
al.; "Adult spinal cord stem cells generate neurons after transplantation in
the adult dentate gyrus," J Neuroscience 20, 8727-8735; December 2000.
Barnett et al.; "Identification of a human olfactory ensheathing cell
that can effect transplant-mediated remyelination of demyelinated CNS
axons," Brain 123, 1581-1588, August 2000
A. Ramon-Cueto et al., "Long-distance axonal regeneration in the
transected adult rat spinal cord is promoted by olfactory ensheathing glial
transplants," J Neuroscience 18, 3803-3815; May 15, 1998 |
Embryonic Stem Cells A study by McDonald et al. study showed some
functional improvement in rats with spinal cord injury, slightly better than no
treatment alone.Studies by Liu et al. and Brüstle et al. showed that ES cells
could form protective myelin sheaths around nerves in rats with spinal cord, but
they did not show or test for any functional recovery of the animals.
References
J.W. McDonald et al., "Transplanted embryonic stem cells survive, differentiate
and promote recovery in injured rat spinal cord," Nature Medicine 12, 1410-1412,
December 1999
S. Liu et al., "Embryonic stem cells differentiate into oligodendrocytes and
myelinate in culture and after spinal cord transplantation," Proc. Natl. Acad.
Sci. USA 97, 6126-6131; May 23, 2000
O. Brüstle et al., "Embryonic Stem Cell-Derived Glial Precursers: A Source of
Myelinating Transplants," Science 285, 754-756, July 30, 1999 |
|
Diabetes |
|
Adult Stem Cells Scientists
"retrained" immune cells to reverse diabetes in mice. The autoimmunity that
was previously directed against insulin-secreting cells was reversed, and
adult stem cells in the mice formed insulin-secreting cells. The treatment
was "…thus able to effect an apparent cure of established Type 1 diabetes in
the [diabetic] mouse" (S. Ryu et al.).
Pancreatic adult stem cells grown in culture formed insulin-secreting
islets. When injected into diabetic mice, the mice survived without further
need of insulin injections.
Scientists at Harvard Medical School cultured human pancreatic ductal
cells under specific conditions, inducing the cells to form islet buds and
secrete insulin. "Thus, duct tissue from human pancreas can be expanded in
culture and then be directed to differentiate into glucose responsive islet
tissue in vitro. This approach may provide a potential new source of
pancreatic islet cells for transplantation"
References
S. Ryu et al.; "Reversal of established autoimmune diabetes by restoration
of endogenous ß cell function," J. Clin. Invest. 108, 63-72; July 2001
V.K. Ramiya et al.; "Reversal of insulin-dependent diabetes using islets
generated in vitro from pancreatic stem cells," Nature Medicine 6, 278-282,
March 2000.
S. Bonner-Weir et al.; "In vitro cultivation of human islets from
expanded ductal tissue," Proc Natl Acad Sci USA 97, 7999-8004; July 5, 2000. |
Embryonic Stem Cells
Researchers
reported the apparent conversion of mouse embryonic stem cells into insulin
producing pancreatic islet cells. The mouse embryonic stem cells secreted
only 1/50th the normal amount of insulin, and diabetic mice implanted with
the cells still died.
Reference
N. Lumelsky et al.; "Differentiation of embryonic stem cells to
insulin-secreting structures similar to pancreatic islets," Science 292,
1389-1394; May 18, 2001 |
|
