408
Electromagnetic Fields in Biological Systems
that we used the highest irradiance that has been reported to date (e.g., ∼2500 times
greater than most previous studies). Moreover, because our hyperthermic-exposed cells
also showed signs of death, these findings further confirm that the THz-induced cell
death that we observed is mediated primarily via photothermal mechanisms.
7.5.5 Direct Effects of Terahertz Radiation on
Cellular Organelles and Biomolecules
In addition to the conflicting results reported at a cellular level, the data in Table 7.2
also suggest that mixed conclusions have been drawn regarding the impact of THz
on cellular organelles and intracellular biomolecules (e.g., lipids, proteins, and DNA).
For instance, Ramundo-Orlando et al. showed that pulsed THz radiation can directly
affect the permeability of liposomes (Ramundo-Orlando et al. 2007). This observation
is quite intriguing, and it will be interesting to see if future investigations observe similar effects in mammalian cells. In addition to lipids, Homenko et al. have also shown
that THz radiation can affect protein activity in an antigen–antibody model (Homenko
et al. 2009). Consistent with this finding, our research group recently observed that
THz-exposed cells dramatically increase their intracellular HSP expression. Since HSP
upregulation is a hallmark condition for intracellular protein damage, our observations
suggest that THz radiation causes significant intracellular protein damage. However, we
have not yet conducted definitive experiments to determine whether HSP upregulation
is a result of direct protein damage (primary effect) or is caused by the temperature rise
that generated during THz irradiation (secondary effect).
7.5.6 Genotoxic Effects of Terahertz Radiation
Mixed conclusions have also been drawn on the effect that THz radiation exerts on DNA.
For instance, both Scarfi et al. (Scarfi et al. 2003) and Zeni et al. (Zeni et al. 2007) showed
that THz radiation does not induce genotoxicity, while Korenstein-Ilan et al. (KorensteinIlan et al. 2008) observed signs of aneuploidy (i.e., genomic instability). Although all of
these studies used roughly the same frequency (∼0.1 THz) and the same cell line (lymphocytes), a few fundamental differences exist between them that may account for these
conflicting results. First, Korenstein-Ilan et al. exposed cells for considerably longer exposure durations than used in Scarfi et al. 2003 and Zeni et al. 2007—1440 minutes rather
than 20 minutes. Second, the groups used very different sources in their experiments:
Korenstein-Ilan et al. used a frequency multiplier unit that generates incoherent CW THz
radiation, whereas Scarfi and Zeni et al. both used a FEL that generates coherent, pulsed,
broadband THz radiation (Scarfi et al. 2003; Zeni et al. 2007). To date, it is still not clear
which of these properties may be responsible for these conflicting results.
7.5.7 Does Terahertz Radiation Trigger Signature
Gene Expression Profiles in Human Cells?
In this final section, we provide data that our group recently collected. Our main goal
for these experiments was to determine whether human cells activate a signature gene
Electromagnetic Fields in Biological Systems
that we used the highest irradiance that has been reported to date (e.g., ∼2500 times
greater than most previous studies). Moreover, because our hyperthermic-exposed cells
also showed signs of death, these findings further confirm that the THz-induced cell
death that we observed is mediated primarily via photothermal mechanisms.
7.5.5 Direct Effects of Terahertz Radiation on
Cellular Organelles and Biomolecules
In addition to the conflicting results reported at a cellular level, the data in Table 7.2
also suggest that mixed conclusions have been drawn regarding the impact of THz
on cellular organelles and intracellular biomolecules (e.g., lipids, proteins, and DNA).
For instance, Ramundo-Orlando et al. showed that pulsed THz radiation can directly
affect the permeability of liposomes (Ramundo-Orlando et al. 2007). This observation
is quite intriguing, and it will be interesting to see if future investigations observe similar effects in mammalian cells. In addition to lipids, Homenko et al. have also shown
that THz radiation can affect protein activity in an antigen–antibody model (Homenko
et al. 2009). Consistent with this finding, our research group recently observed that
THz-exposed cells dramatically increase their intracellular HSP expression. Since HSP
upregulation is a hallmark condition for intracellular protein damage, our observations
suggest that THz radiation causes significant intracellular protein damage. However, we
have not yet conducted definitive experiments to determine whether HSP upregulation
is a result of direct protein damage (primary effect) or is caused by the temperature rise
that generated during THz irradiation (secondary effect).
7.5.6 Genotoxic Effects of Terahertz Radiation
Mixed conclusions have also been drawn on the effect that THz radiation exerts on DNA.
For instance, both Scarfi et al. (Scarfi et al. 2003) and Zeni et al. (Zeni et al. 2007) showed
that THz radiation does not induce genotoxicity, while Korenstein-Ilan et al. (KorensteinIlan et al. 2008) observed signs of aneuploidy (i.e., genomic instability). Although all of
these studies used roughly the same frequency (∼0.1 THz) and the same cell line (lymphocytes), a few fundamental differences exist between them that may account for these
conflicting results. First, Korenstein-Ilan et al. exposed cells for considerably longer exposure durations than used in Scarfi et al. 2003 and Zeni et al. 2007—1440 minutes rather
than 20 minutes. Second, the groups used very different sources in their experiments:
Korenstein-Ilan et al. used a frequency multiplier unit that generates incoherent CW THz
radiation, whereas Scarfi and Zeni et al. both used a FEL that generates coherent, pulsed,
broadband THz radiation (Scarfi et al. 2003; Zeni et al. 2007). To date, it is still not clear
which of these properties may be responsible for these conflicting results.
7.5.7 Does Terahertz Radiation Trigger Signature
Gene Expression Profiles in Human Cells?
In this final section, we provide data that our group recently collected. Our main goal
for these experiments was to determine whether human cells activate a signature gene