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Phototherapy has become more popular and widely used in the treatment of a variety of medical conditions. To
ensure sound results as evidence of its effectiveness, well designed experiments must be conducted when
determining the effect of phototherapy. Cell culture models such as hypoxic, acidotic and wounded cell cultures
simulating different disease conditions including ischemic heart disease, diabetes and wound healing were used to
determine the effect of laser irradiation on the genetic integrity of the cell.
Even though phototherapy has been found to be beneficial in a wide spectrum of conditions, it has been shown to
induce DNA damage. However, this damage appears to be repairable. The risk lies in the fact that phototherapy
may help the medical condition initially but damage DNA at the same time leaving undetected damage that may
result in late onset, more severe, induced medical conditions including cancer.
Human skin fibroblasts were cultured and used to induce a wound (by the central scratch model), hypoxic (by
incubation in an anaerobic jar, 95% N2 and 5% O2) and acidotic (reducing the pH of the media to 6.7) conditions.
Different models were irradiated using a Helium-Neon (632.8 nm) laser with a power density of 2.07 mW/cm2 and a
fluence of 5 J/cm2 or 16 J/cm2. The effect of the irradiation was determined using the Comet assay 1 and 24 h after
irradiation. In addition, the Comet assay was performed with the addition of formamidopyrimidine glycosylase
(FPG) obviating strand brakes in oxidized bases at a high fluence of 16 J/cm2.
A significant increase in DNA damage was seen in all three injured models at both 1 and 24 h post-irradiation when
compared to the normal un-injured cells. However, when compared to non-irradiated controls the acidotic model
showed a significant decrease in DNA damage 24 h after irradiation indicating the possible induction of cellular
DNA repair mechanisms. When wounded cells were irradiated with higher fluences of 16 J/cm2, there was a
significant increase in DNA damage in irradiated cells with and without the addition of FPG. These results are
indicative of the importance of both cell injury model as well as fluence when assessing the effect of phototherapy
on DNA integrity.
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