Biomedical Engineering Reference
In-Depth Information
cardiac function in coronary diseases, revealed that injection of
autologous myoblasts in combination with coronary artery bypass
surgery significantly reduced left ventricular volume but did not
alter left ventricular ejection fraction any more than the control
treatment (surgery only) [33]. Considering that approximately
80% of directly transplanted myoblasts reportedly disappear 24
hours after transplantation [34], insufficient engraftment of skeletal
myoblasts and the resulting shortage of growth factors secreted
from these cells may account for the insufficient effects. In search
of a more efficient transplantation procedures, Dr. Sawa's group
prepared skeletal myoblast sheets using culture dishes coated with a
temperature-responsive polymer and tested them in a rat myocardial
infarct model [31], dilated cardiomyopathic hamsters [30], and a
canine dilated cardiomyopathy-like model [29]. On the basis of the
myocardial repair and improvement of cardiac function observed
in these models, myoblast sheets are currently being investigated
in a clinical trial. Moreover, implantation of the myoblast sheets
was shown to be more effective than direct injection of myoblasts
into the myocardium in suppressing fibrosis and in improving left
ventricular ejection fraction in a rat model of ischemia [35]. These
findings suggest that efficient engraftment of the transplanted cells
is crucial for sustained paracrine effects.
2a.6
Cardiac Stem/Progenitor Cells
The notion of the heart as a terminally differentiated organ with
no self-repair potential has been undermined by recent studies
demonstrating the presence of cardiac stem/progenitor cells
that can differentiate into cardiomyocytes in the heart of adult
mammals, including humans. Also, since self-repair in the heart
was recently observed in humans [36], the presence of self-repair
mechanisms mediated by endogenous cardiac stem/progenitor
cells is now becoming an accepted concept. Accordingly, cardiac
stem/progenitor cells possibly improve cardiac function by
differentiating into cardiomyocytes, and therefore they are thought
to be a more promising candidate for transplantation than many
other cells. There are several subtypes of cardiac stem/progenitor
cells, including c-kit-positive cells [37], Sca-1-positive cells [38,
39], side population cells [40], isl-1-positive cells [41], and cardiac
