| ARVID CARLSSON´S COLUMN
News and reports about stem cell research are
frequent in the media, often with optimistic
overtones. The public gets the impression that
brain repair by stem cells will soon be possible.
But many reports are biased and tend to ignore
important negative results. This is true, for
example, of the regeneration of nerve cells
(neurogenesis) in the brain of human adults, and
of the role of stem cells in depression, learning
and stroke. (Read about studies in Lena´s column.)
Regeneration of
nerve cells is not confirmed
It is often stated as an established truth
that new nerve cells can replace lost cells even
in the adult human brain. But this statement
remains unproven today. In 1998 Peter Eriksson
and his colleagues at the University of
Gothenburg claimed that new neurons can be formed
in the hippocampus of the temporal lobe in adult
humans. However, in 2001 the Hungarian scientist
Laszlo Seress, using markers for cell division,
saw a dramatic decline in cell proliferation in
human hippocampus after the first year of life.
He could not confirm that any of the cells were
neurons.
In the Swedish newspaper Dagens Nyheter in
October 2006, the science editor wrote that Jonas
Frisén at the Karolinska Institute had succeeded
in corroborating Eriksson´s finding of
neurogenesis in the hippocampus, using a new
method to determine the age of nerve cells. But
Frisén´s investigation has not yet been
published or even submitted for publication. His
study was still going on when the article
appeared in Dagens Nyheter. Since then nothing
important has happened, according to Frisén
(personal communication to Lena Carlsson in the
middle of December 2006).
In their studies Peter Eriksson and Jonas Frisén
are using different techniques to demonstrate
neurogenesis. Eriksson utilizes components
resembling DNA, and Frisén a technique based on
radioactive carbon. Both techniques are measuring
material being incorporated into the DNA of
dividing cells. It is important to know that such
incorporation can occur even in the absence of
new nerve cell formation. The results are
conclusive only if they are negative, that is, if
there is no incorporation, and no new neurons
have been formed (see Lena´s column).
The picture is far
too positive
As the many serious problems in stem cell
research are seldom fully exposed, the picture
available to the public is far too glossy. This
is not least true of the prospects of cell
transplantation in Parkinson´s disease. When
Swedish scientists, for example, report on the
state of the art in this field they tend to
ignore that the two largest and best controlled
and analyzed transplantation studies in
Parkinson's disease show quite discouraging
results, as already commented upon in my previous
column.
Admittedly some prominent stem cell researchers
mention the great obstacles that must be overcome
if stem cell therapy in patients is to become a
reality. However, they do not seem to be very
anxious to communicate their concern to laymen,
such as patients, the general public, granting
institutions, or politicians.
A century ago the Nobel Laureate Ramon y Cajal
stated that lost nerve cells cannot be replaced.
He has not yet been proven wrong. Needless to
say, however, his statement was limited to nerve
cells. For many other cell types the prospects
could be very different.
January, 2007
Arvid Carlsson
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