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. Author manuscript; available in PMC: 2018 Jun 1.
Published in final edited form as: Tumour Biol. 2017 Jun;39(6):1010428317706913. doi: 10.1177/1010428317706913

Figure 2.

Figure 2

Proposed mechanism of the biphasic dose effect of LILI treatment on CSCs. Light photon from laser is absorbed by the cytochrome c oxidase (COX) of the respiratory chain. The energy of photons donated by low-fluence visible red light is sufficient to dissociate nitric oxide (NO) from COX and enhance the COX reduction capacity which eventually leads to CSC proliferation through ATP, cAMP, and moderate ROS production. By contrast, the energy of photons donated by high-fluence visible red light is sufficient to decrease the COX reduction capacity leading to the massive conversion of dioxygen into ROS which prompts the programmed cell death. High level of ROS within the inner membrane of the mitochondria serves as signal for the opening of the mitochondrial permeability which triggers caspase-3 activation leading to the release of COX in the outer membrane which in turn serves as signal for the activation of pro-apoptotic enzymes.