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Terahertz Radiation
In regard to the first question, most studies associated with the THz-Bridge project
found that THz-induced bioeffects are mediated primarily via photothermal mechanisms (i.e., thermal effects). This finding is not surprising given the fact that THz frequencies are known to be strongly absorbed by water, the main constituent and primary
tissue chromophore at THz frequencies (Wilmink et al. 2011).
In contrast, mixed results were reported for the second question regarding the genotoxic nature of THz radiation (Berns and Bewley 1987; Scarfi et al. 2003; Zeni et al. 2007;
Korenstein-Ilan et al. 2008). For example, Korenstein-Ilan et al. (Korenstein-Ilan et al.
2008) observed both genotoxic and epigenetic effects in lymphocytes exposed to 0.1 THz
radiation, whereas neither of these effects were observed in other comparable studies (Scarfi
et al. 2003; Zeni et al. 2007). In addition to affecting DNA, several studies report that THz
radiation can also impair intracellular protein and enzymatic processes (Cherkasova et al.
2009; Homenko et al. 2009). These findings are particularly compelling because the energy
of THz photons is not high enough to directly disrupt chemical bonds. All in all, the THzBridge project made several landmark discoveries in the area of research on THz bioeffects.
In addition, the project served to raise several poignant questions regarding the mechanism
by which THz radiation interacts, couples, and subsequently damages biomolecules.
7.5.3 Recent Studies on Terahertz Bioeffects (2004–2010)
Since 2004, theoretical models have been developed that postulate that specific THz frequencies may be able to couple directly to biomolecules via coherent excitations (Frohlich
1975) and/or nonlinear resonance mechanisms (Chitanvis 2006; Alexandrov et al. 2009).
This coupling mechanism is believed to be due to that fact that THz radiation (i.e.,
THz = 10 12 Hz) oscillates on the same timescale as the natural phonon frequencies of double-stranded DNA (dsDNA) (Chitanvis 2006; Alexandrov et al. 2009). Furthermore, such
coupling has been suggested to lead to the creation of localized openings (bubbles) between
the DNA strands (Chitanvis 2006; Alexandrov et al. 2009). In turn, these openings then
drive the dsDNA to “unzip,” thereby interfering with normal transcription processes.
Since these processes could cause biological effects, which may not be fully attributable
to conventional thermal effects, these studies have motivated researchers to reconsider
the concept of “microthermal” or “nonthermal” effects. In addition, these studies have
contributed to the emergence of several fundamental questions: (1) Do mammalian cells
exposed to specific THz exposure conditions (frequency, exposure duration, irradiance,
pulsed vs. CW, etc.) exhibit specific cellular effects (i.e., morphological changes, viability,
growth kinetics)? (2) What direct impact does THz radiation have on cellular plasma
membranes and intracellular biomolecules (i.e., lipids, proteins, and DNA)? (3) Is THz
radiation genotoxic to mammalian cells, and if so, at what exposure conditions are such
effects observed? and (4) Do mammalian cells exposed to THz radiation exhibit a signature gene expression profile that is not observed in hyperthermic-treated cells?
In an effort to guide a discussion which addresses the above questions, we have created
a table that summarizes the findings from most THz bioeffects studies that have been conducted to date. (Table 7.2; Clothier and Bourne 2003; Fedorov et al. 2003; Scarfi et al. 2003;
Ramundo-Orlando et al. 2007; Zeni et al. 2007; Korenstein-Ilan et al. 2008; Olshevskaya
et al. 2008; Cherkasova et al. 2009; Homenko et al., 2009.) In this table, we provide the