Biomedical Engineering Reference
In-Depth Information
Fig. 2.36.
Fluoresence labeled vectors (DNA) and their products (GFP). The vec-
tors were introduced into the cell by ultrasound. Then cells transcripted them and
synthesized fluorescent protein
amount of introduced gene. This suggests that ultrasound exposure has ef-
fects on cellular properties in addition to changing the permeability of the
membrane (Fig. 2.36).
2.6.5
Direct Effects on Cell Components
The mutagenic activity of radiation is well known and is mainly explained by
damage to DNA. Any kind of energy may lead to the same effect on biological
materials as radiation. Fragmentation of genomic DNA was assayed by gel
electrophoresis study. Smaller DNA fragments that have a smaller molecular
size move greater distances than unfragmented DNA. The electrophoresis
pattern of the cell exposed to ultrasound showed a fragmented DNA tail,
while the pattern of the untreated cell did not (Fig. 2.37).
This result indicates that ultrasound exposure causes DNA damage. Free
radicals and hydrogen peroxide that are generated by the cavitation effect of
ultrasound may cause DNA damage just as radiation does. Nevertheless, this
hypothesis is likely to be supported: the lifetime of the free radicals is too
short to allow them to reach the nucleus DNA from the cell membrane. There
is no clear evidence that cavitation may occur inside a cell at the acoustic
power used in diagnosis today. Thus, we should consider another hypothesis,
that DNA damage results from cellular activity.
2.6.6 The Stress-Induced Cellular Response
A mammalian cell has a sophisticated system to repair damaged DNA. Severe
DNA damage does not allow expression of any gene, even for repair, which
