“Good” and “Bad” Free Radicals in Photobiostimulation

Abstract

There is now considerable evidence that photobiostimulation proceeds via enhanced production of reactive oxygen species (ROS) by the photoexcited respiratory chain (RC). The most commom of these ROS is the superoxide anion radical which is also pruduced normally in the reduction of oxygen by the RC. On the other hand, increased amounts of free radicals are produced in the blood of patients with acute respiratory illness or leukemia. Surprisingly, irradiation with low energy doses of 633 or 830 nm laser light reduces the amount of free radicals produced in the anomalous blood cells. We propose to explain this surprising result by subdividing the free radicals into two categories: (a) the “good” ones which may produce biostimulation and which we tentatively take to be the superoxide anion radicals and (b) the “bad” ones which we collectively designate by R. The reduction of the quantity of free radicals by photobiostimulation is then ascribed to the reaction

R^. + O₂’ ′ → R ′ ’+ O₂.