In vitro human cell responses to a low-dose photodynamic treatment vs. mild H2O2 exposure

• Low-dose short-time ROS exposure increases in vitro human cell proliferation.
• The observed mitotic enhancement is transient after ROS exposure.
• H2O2 at low concentration greatly increases micronuclei frequency.
• Low-dose PDT treatment does not induce micronuclei increase.

Photodynamic treatments allow control of the amount of reactive oxygen species (ROS) produced through the photosensitizer concentration and the light dose delivered to the target. In this way low ROS doses can be achieved in situ to study cell responses related to redox regulation. In this study a comparison has been made between different cell responses to a low-dose photodynamic treatment and both low and relatively high concentrations of H2O2 in human immortalized keratinocytes (HaCaT). The obtained results show that the photodynamic treatment induces a stimulating cell response roughly equivalent to that produced by exposing cells to 10−5 M H2O2. Higher H2O2 concentrations gave rise to concentration-dependent deleterious effects on the cell cultures. Of importance is that the photodynamic treatment did not produce genotoxic damage, as measured by micronuclei frequency, while cultures exposed to 10−5 M H2O2 displayed a significant increase in the amount of cells with micronuclei. In summary, the low-dose photodynamic treatment promotes cell proliferation but does not incur in the excessive clastogenic lesions observed after H2O2 exposure. It is therefore proposed as a promising alternative to direct H2O2 exposure in the study of cell redox signalling.

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